The characteristics and antioxidative activities of yellow and black soybean cheonggukjang prepared with theaddition of purple sweet potato (Ipomoea batatas cv. Jami) were evaluated. In sensory evaluation experiments involvingthe addition of purple sweet potatoes to cheonggukjang at 0, 5, 10, 20, and 30% ratios (w/w), yellow (YCAP) and black(BCAP) soybean cheonggukjang with 20% purple sweet potato were most preferred. The total phenolics and flavonoidcontents of YCAP and BCAP were higher than those of yellow (YC) and black (BC) cheonggukjang prepared withoutadded purple sweet potato. YCAP and BCAP also showed higher DPPH radical-scavenging activities than other samples. Moreover, rat blood plasma samples taken 1 h after oral administration of YCAP and BCAP showed higher inhibitoryeffects against lipid peroxidation than did rats fed YC or BC. These results suggest that the long-term intake ofcheonggukjang prepared with purple sweet potato may increase the antioxidative activity in the blood.