Natural methane on Mars refers to reports of detection of methane (CH₄) in Mars's atmosphere. The potential presence of methane in the atmosphere of Mars may indicate the presence of microbial life or geological activity.

Mars orbiters and rovers, as well as Earth-based telescopes, have used infrared spectroscopy to search for trace amounts of methane in Mars's atmosphere. Measurements of methane from 60 ppbv to under the detection limit (<0.05 ppbv) have been reported, but there is no scientific consensus on whether these observations genuinely corroborate the existence of methane on Mars.

In 1969, the Mariner 7 science team reported in a press conference that methane and ammonia had been detected near the Marian polar ice cap. However, that claim was retracted after subsequent analyses revealed that the spectral signals were actually produced by carbon dioxide ice. Subsequent measurements of the chemistry of the Mars atmosphere by Mariner 9 did not detect methane, placing its upper limit at 20 ppbv.

Three ground-based telescope teams reported extended plumes of methane on Mars in the summer of 2003. Detection of Mars methane (10±3 ppbv) was also reported at the Canada–France–Hawaii Telescope in 2004. Earth-based measurement of Mars looks through Earth's atmosphere, and telluric contamination from terrestrial methane is present in the measurement. Thus, these studies involved filtering out spectral lines for both CH₄ and H₂O in the Earth's atmosphere. However, critics argued that many of the Doppler-shifted methane lines were still too close to telluric lines for water and other gases. The close proximity between telluric spectral lines and potential Martian spectral lines raised concerns about relying solely on one wavelength for methane detection. Subsequent ground-based telescope observations did not detect methane or methane oxidation products, with upper limits for methane of 7 ppbv.

In 2004, the science team of the Planetary Fourier Spectrometer on ESA's Mars Express orbiter reported detection of methane in Mars's atmosphere at a global average concentration of 10±5 ppbv, and peak abundances of 30 ppbv. These claims were later disputed on technical grounds related to instrumentation resolution and data-fitting. The Mars Global Surveyor reported contemporaneous confirmation of a spike in methane (16±3 ppbv) in Gale crater on 16 June 2013 (see Curiosity rover below).

In 2010, the science team of the Thermal Emission Spectrometer on the Mars Global Surveyor reported detectable methane (5 to 33 ppbv) that seemed to vary seasonally. However, subsequent data validation was not able to definitively confirm the presence of methane in the previous report.

In August 2012, NASA's Curiosity rover landed on Mars in Gale crater with the Tunable Laser Spectrometer instrument capable of making precise methane abundance measurements. Initial data found no detectable methane (<1.3 ppbv) in the atmosphere of Gale Crater. A rise from <1 to 7±2 ppbv was observed from 2013 to 2014, followed by a drop back down to baseline levels, suggesting that Gale Crater may be episodically releasing methane from an unknown source. In 2018, the science team reported seasonal variation of methane in Gale Crater, from 0.2 to 0.7 ppbv. However, the statistical validity of the claims was disputed, and reanalysis showed no significant seasonal variation. In 2021, the science team reported day-night variation at Gale crater, from 0.05±0.22 ppbv in the day to 0.5±0.1 ppbv at night. In 2025, the possibility of leaks of terrestrial methane in the foreoptics chamber of the Tunable Laser Spectrometer was presented as a potential explanation for previous methane measurements by the rover.

In 2016, the Stratospheric Observatory for Infrared Astronomy made spectral observations of the Martian atmosphere from Earth's stratosphere during the Martian summer in its northern hemisphere. When processing the data, care was taken to minimize interference from Earth-based methane spectral lines, and long observation times were used to increase signal-to-noise ratio. No methane was detected.