A protein which is capable of depolymerizing F-actin was purified from an extract of unfertilized starfish eggs by the use of DEAE-cellulose column chromatography and hydroxylapatite column chromatography. This protein has an apparent molecular weight of 17, 000. It inhibited the extent of actin polymerization as well as depolymerizing F-actin rapidly. It was shown that this protein reacts with actin at a molar ratio of 1:1. The properties of this protein were compared with those of profilin from mammalian tissues.