The compound 4-cyclopropylmethyleneoxy-3-chlorophenylacetic acid and its non-toxic pharmaceutically acceptable salts have activity as anti-inflammatory, antipiretic and analgesic agents. It is prepared by reacting a lower alkyl ester of 3-chloro-4-hydroxyphenyl acetic acid with a cyclopropylmethylene halide and subsequently saponifying the ester obtained. The acid obtained is optionally salified to give corresponding non-toxic, inorganic or organic pharmaceutically acceptable salts.