PROBLEM TO BE SOLVED: To provide a platelet aggregation inhibiting substance which is obtained by making a fermentation object making a genus Rhizopus as a spawn as a raw material. SOLUTION: The strong platelet aggregation inhibitory activity in a fraction extracted by an atmospheric distillation is recognized. The substance is a low molecular fraction which is stable to heat and has a fresh scent with colorlessness. Such an activity is not seen at all in natto (fermented soybeans). Moreover, it is found that the platelet aggregation inhibiting substance is also obtained by shaking/culturing a tempe bacillus. COPYRIGHT: (C)2011,JPO&INPIT