Thiophene-3-acetic acid is an organosulfur compound with the formula HO<sub>2</sub>CCH<sub>2</sub>C<sub>4</sub>H<sub>3</sub>S. It is a white solid. It is one of two isomers of thiophene acetic acid, the other being thiophene-2-acetic acid.
Thiophene-3-acetic acid has attracted attention as a precursor to functionalized derivatives of polythiophene.