An attempt to use combination therapy with anti-tumor necrosis factor α (TNFα) antibodies and tacrolimus (TAC) has been tried to induce remission in ulcerative colitis (UC). However, the optimal dose of TAC in combination therapy with anti-TNFα antibodies (TAC + anti-TNFα therapy) remains unclear. We examined the efficacy of various doses of TAC + anti-TNFα therapy in a mouse colitis model. Dextran sulfate sodium induced colitis model mice were divided into an anti-TNFα antibody monotherapy group and the groups that received various doses of TAC + anti-TNFα therapy. The nuclear factor expression of activated T-cells, cytoplasmic 1 (NFATc1) in the nuclei and the mRNA expression of inflammatory cytokines were assessed by immunohistochemistry and RT-PCR, respectively. The serum anti-TNFα antibody concentration was measured with an enzyme-linked immunosorbent assay. The colon length and histological severity were significantly improved in the groups that received any dose of TAC + anti-TNFα therapy. The nuclear expression of NFATc1 was inversely proportional to the administered doses of TAC. The expression levels of inflammatory cytokines tended to decrease in proportion to the dose of TAC. The serum concentration of anti-TNFα antibodies in the high-dose TAC + anti-TNFα therapy was significantly higher than those in the other groups. Low-dose TAC exerted its immunosuppressive effect on T-cells, and additionally, high-dose TAC maintained the serum anti-TNFα antibody concentration. When administered in combination with anti-TNFα antibodies, the dose of TAC should be adjusted according to the disease severity.