Ganjang and doenjang are known as major fermented soy-based foods in Koreans. Current investigations have proved that fermented soybean foods impart anti-cancer, anti-obesity, and anti-diabetic effects. The aim of this study was to evaluate the anti-cancer activities of commercialized soy food, Ganjang, as a function of aging period. The test groups were classified into four time periods-short (under 5 years, S group), mid (under 10 years, M group), long (under 15 years, L group), and eternal (over 15 years, E group). The anti-cancer effects of Ganjang were determined by cell cytotoxicity assay of three types of cancer cell lines and splenocyte proliferation assay. Besides these assays, we also analyzed NK cell activity for cancer immunotherapy. The results show that the anti-cancer effect increased in the S and M period aging groups for all three cancer cell lines. Interestingly, similar to the anti-cancer result, splenocyte proliferation and NK activity showed the highest effect in the S and M groups. In contrast, Japanese ganjang-treated (JG1, JG2) groups and E group showed significantly reduced splenocyte proliferation. Collectively, these results suggest that the short and middle periods of traditional fermented Ganjang might have potential anti-cancer activities.