A method for producing prostaglandins comprises converting unsaturated fatty acids contained in an alga belonging to genus Gracilaria or genus Hypnea into prostaglandins by the action of an enzyme present in the alga in water or a water-containing solvent so that the prostaglandins are released from the alga into the water or the water-containing solvent and then recovering the prostaglandins from the solvent; or comprises adding an unsaturated fatty acid to water or a water-containing solvent, converting the unsaturated fatty acid into prostaglandins by the action of the enzyme present in the alga belonging to genus Gracilaria or genus Hypnea in the solvent and then recovering prostaglandins from the solvent. The purification of prostaglandins can effectively be performed by a method which comprises contacting a solution of prostaglandins in water or a water-containing organic solvent with a non-polar porous synthetic resin having a specific surface area of not less than 350 m²/g and a fine pore volume of not less than 0.8 mℓ /g to thus adsorb the prostaglandins to the resin and then eluting the adsorbed prostaglandins with an organic solvent or a water-containing organic solvent for elution. The method makes it possible to provide desired prostaglandins in high yield and to produce prostaglandins in industrial scale.