Martian soil is the fine regolith found on the surface of Mars. Its properties can differ significantly from those of terrestrial soil.

The term Martian soil typically refers to the finer fraction of regolith, that which is composed of grains one centimeter in diameter or less. Some have argued that the term "soil" is not correct in reference to Mars because soil is defined as having organic content, whereas Mars is not known to have any. However, standard usage among planetary scientists is to ignore that distinction. Martian dust generally connotes even finer materials than Martian soil, the fraction which is less than 30 micrometres in diameter. Disagreement over the significance of soil's definition arises due to the lack of an integrated concept of soil in the literature. The pragmatic definition "medium for plant growth" has been commonly adopted in the planetary science community but a more complex definition describes soil as (bio)geochemically/physically altered material at the surface of a planetary body that encompasses surficial extraterrestrial telluric deposits. This definition emphasizes that soil is a body that retains information about its environmental history and that does not need the presence of life to form.