Venera 4 (Russian: Венера-4, lit. 'Venus-4'), also designated 4V-1 No.310, was a probe in the Soviet Venera program for the exploration of Venus. The probe comprised a lander, designed to enter the Venusian atmosphere and parachute to the surface, and a carrier/flyby spacecraft, which carried the lander to Venus and served as a communications relay for it.

In 1967, it was the first successful probe to perform in-place analysis of the environment of another planet. Venera 4 provided the first chemical analysis of the Venusian atmosphere, showing it to be primarily carbon dioxide with a few percents of nitrogen and below one percent of oxygen and water vapors. While entering the atmosphere it became the first spacecraft to survive entry into another planet's atmosphere. The station detected a weak magnetic field and no radiation field. The outer atmospheric layer contained very little hydrogen and no atomic oxygen. The probe sent the first direct measurements proving that Venus was extremely hot, that its atmosphere was far denser than expected, and that it had lost most of its water long ago.

The main carrier spacecraft 4 stood 3.5 metres (11 ft) high, its solar panels spanned 4 metres (13 ft) and had an area of 2.5 square metres (27 sq ft). The carrier spacecraft included a 2 metres (6 ft 7 in) long magnetometer, an ion detector, a cosmic ray detector and an ultraviolet spectrometer capable of detecting hydrogen and oxygen gases. The devices were intended to operate until entry into the Venusian atmosphere. At that juncture, the station was designed to release the probe capsule and disintegrate. The rear part of the carrier spacecraft contained a liquid-fuel thruster capable of correcting the flight course. The flight program was planned to include two significant course corrections, for which purpose the station could receive and execute up to 127 different commands sent from the Earth.

The front part of the carrier spacecraft contained a nearly spherical landing capsule 1 metre (3 ft 3 in) in diameter and weighing 383 kilograms (844 lb). Compared to previous (failed) Venera probes, the capsule contained an improved heat shield that could withstand temperatures up to 11,000 °C (19,800 °F). Instead of the previous liquid-based cooling design, a simpler and more reliable gas system was installed. The durability of the capsule was checked by exposing it to high temperatures, pressures, and accelerations using three unique testing installations. The heat resistance was checked in a high-temperature vacuum system emulating the upper layers of the atmosphere. The capsule was pressurized up to 25 atmospheres. (The surface pressure on Venus was unknown at the time. Estimates ranged from a few to hundreds of atmospheres). Finally, it was subjected to accelerations of up to 450 g in a centrifuge. The centrifuge test caused cracking of electronic components and cable brackets, which were replaced shortly before launch. The timing for the launch was rather tight, so as not to miss the launch window — the days of the year when the path to the destination planet from Earth is energetically least demanding.

The capsule could float in case of a water landing. Considering the possibility of such a landing, its designers made the lock of the capsule using sugar; it was meant to dissolve in liquid water, releasing the transmitter antennas. The capsule contained a newly developed vibration-damping system, and its parachute could resist temperatures up to 450 °C (723 K).

The capsule contained an altimeter, thermal control, a parachute and equipment for making atmospheric measurements. The latter included a thermometer, barometer, hydrometer, altimeter and a set of gas analysis instruments. The data were sent by two transmitters at a frequency of 922 MHz and a rate of 1 bit/s; the measurements were sent every 48 seconds. The transmitters were activated by the parachute deployment as soon as the outside pressure reached 0.6 standard atmospheres (61 kPa), which was thought to occur at the altitude about 26 kilometres (16 mi) above the surface of the planet. The signals were received by several stations, including the Jodrell Bank Observatory.

The capsule was equipped with a rechargeable battery with a capacity sufficient for 100 minutes of powering the measurement and transmitter systems. To avoid becoming discharged during the flight to Venus, the battery was kept charged using the solar panels of the carrier spacecraft. Before the launch, the entire Venera 4 station was sterilized to prevent possible biological contamination of Venus.

Two nominally identical 4V-1 probes were launched in June 1967. The first probe, Venera 4, was launched on 12 June by a Molniya-M carrier rocket flying from the Baikonur Cosmodrome. A course correction was performed on 29 July when it was 12,000,000 kilometres (7,500,000 mi) away from Earth; otherwise, the probe would have missed Venus. Although two such corrections had been planned, the first one was accurate enough and therefore the second correction was canceled. On 18 October 1967, the spacecraft entered the Venusian atmosphere with an estimated landing place near 19°N 38°E / 19°N 38°E / 19; 38. The second probe, Kosmos 167, was launched on 17 June but failed to depart low Earth orbit.