PURPOSE: To efficiently produce 2-thiopheneacetic acid under condition of ordinary temperature under ordinary pressure, by converting 2-thiopheneacetonitrile by action of a microorganism having nitrilase activity.

CONSTITUTION: 2-Thiopheneacetonitrile is converted into 2-thiopheneacetic acid by action of a microorganism having nitrilase activity. Insoluble substances, such as microorganisms, are then removed and solvent extraction, crystallization, etc., are simultaneously carried out to afford high-purity 2-thiopheneacetic acid. Microorganisms belonging to the genus Corynebacterium, Pseudomonas, Rhodococcus, Chromobacterium, etc., are cited as the microorganism having the nitrilase activity. The concentration of the 2-thiopheneacetonitrile is preferably 0.5W5.0wt.% and the reaction temperature is preferably 15W32°C.