As a continuation of the study on the biological roles of furan fatty acids (F acids) which are still vague, their inhibitory effects on the hemolysis of erythrocytes induced by singlet oxygen were examined. Hemolysis proceeded smoothly in the absence of F acids, but was suppressed significantly and dose dependently in their presence. No significant differences in inhibitory effects on the hemolysis induced by singlet oxygen between tetra-alkylsubstituted F acid (F3) and di-alkylsubstituted F acid (NMF) could be detected. The acids underwent oxidation to give the corresponding diketo-enes, indicating a reaction with singlet oxygen to suppress hemolysis. The inhibitory effects of F acids on hemolysis were compared with those of known singlet oxygen quenchers such as dimethylfuran, alpha-tocopherol, ascorbic acid and uric acid and F acids were found to be the most effective quenchers.