Black soybean seed coat is a rich source of polyphenols reported to have various physiological functions. The present study investigated the potential protective effects of polyphenolic extracts from black soybean seed coat on mutagen-induced DNA damage in Salmonella typhimurium. Results from the Ames test using Salmonella stains revealed that black soybean seed coat extract (BE) at 5000 µg/plate showed neither mutagenicity nor cytotoxicity. In contrast, BE, its component cyanidin 3-glucoside (C3G), or procyanidin-rich BE (PC-rich BE) dose-dependently inhibited B(a)P- and 4NQO-induced mutagenesis in the rank order: C3G > BE > PC-rich BE. At 5 μM/plate, C3G and procyanidins, the major polyphenols in BE, inhibited B(a)P-induced mutagenesis in TA 98 and TA 100 by 28 − 59%. They also inhibited 4NQO-induced mutagenesis by 26 − 56%. Collectively, we found that C3G and procyanidins, which are the main active compounds in BE, effectively protected against DNA mutagenic damage in Salmonella typhimurium.