A Mars suit or Mars space suit is a space suit for EVAs on the planet Mars. Compared to a suit designed for space-walking in the near vacuum of low Earth orbit, Mars suits have a greater focus on actual walking and a need for abrasion resistance. Mars' surface gravity is 37.8% of Earth's, approximately 2.3 times that of the Moon, so weight is a significant concern, but there are fewer thermal demands compared to open space. At the surface the suits would contend with the atmosphere of Mars, which has a pressure of about 0.6 to 1 kilopascal (0.087 to 0.145 psi). On the surface, radiation exposure is a concern, especially solar flare events, which can dramatically increase the amount of radiation over a short time.

Some of the issues a Mars suit for surface operations would face include having enough oxygen for the person as the air is mostly carbon dioxide; in addition the air is also at a much lower pressure than Earth's atmosphere at sea level. Other issues include the Martian dust, low temperatures, and radiation.

One design for a Mars suit from the 2010s, the NASA Z-2 suit, would have electroluminescent patches to help crew members identify one another. Three types of tests planned for the Z-2 include tests in a vacuum chamber, tests in NASA's Neutral Buoyancy Laboratory (a large pool for mimicking zero-g), and tests in a rocky desert area. (See also: Z series space suits.)

The Mars 2020 Perseverance rover has a materials test that is hoped will aid Mars suit development, the SHERLOC experiment; it includes a test target with space suit materials. The test will measure how these suit materials are affected by the Martian environment. Six materials have been chosen for testing: Orthofabric, Teflon, nGimat-coated Teflon, Dacron, Vectran, and Polycarbonate. The test will help select the best materials for future Mars space suits. Orthofabric is a polymeric material composed of a weave of GORE-TEX fibers, Nomex, and Kevlar-29.

NASA tested possible Mars space suit materials by exposing them to Mars-equivalent ultraviolet (UV) radiation for 2500 hours, and then studied how the materials were affected. One of the concerns for the Mars suits is how materials respond to chemically reactive Mars dust and exposure to ultraviolet, especially over the lengths of time and amount of use the suits are expected to function.

One researcher working on a design for Mars surface EVA suits was inspired in part by Medieval armor suits. Some ideas for a Mars suits are a Heads-up display projected in the visor, built-in communications equipment, life support, and a voice-recognition assistant.

Examples of design concerns:

One Mars mission design aspect is whether the Mars suits should also be made to work in space, or should be for the surface only.