二甲基巯基丙酸（英语：Dimethylsulfoniopropionate，缩写DMSP）是一种化学式为(CH₃)₂SCH₂CH₂COO的有机化合物，常以内盐形式存在于海洋浮游植物、海藻以及其它陆生及水生维管植物中。

Dimethylsulfoniopropionate (DMSP), is an organosulfur compound with the formula (CH₃)₂SCH₂CH₂COO. This zwitterionic metabolite can be found in marine phytoplankton, seaweeds, and some species of terrestrial and aquatic vascular plants. It functions as an osmolyte as well as several other physiological and environmental roles have also been identified. DMSP was first identified in the marine red alga Polysiphonia fastigiata by Frederick Challenger and Margaret Simpson (later Dr. Whitaker)