Abstract Tofu (T) was fermented with kimchi seasoning (K) at a ratio of 1:0.5 and 1:1 (w/w) without and with a starter (L) (designated 1:0.5 TK, 1:0.5 TK-L, 1:1 TK and 1:1 TK-L) to utilize as a new type of lactic acid fermented food. A starter strain KL-12 was isolated from kimchi and identified to belong to the Lactobacillus plantarum group. During fermentation of four TK groups for 16 weeks at 20 °C, pH decreased from initial 6.4–6.5 to 4.1–4.6 after 16 weeks, with a remarkable decrease after 1 week. A reversible trend was observed with LAB viable cells. Antioxidant activities of four TK groups increased with fermentation time. After 16 weeks, the 1:1 TK-L group showed higher antioxidant activities (total phenolic content, DPPH and NO scavenging activity) and free amino acids than other three groups. These results indicate the potential use of lactic acid fermented food as a valuable resource for development of functional foods.