BACKGROUND: Full supply of the nutritional requirements of C57BL/6 mice plays an important role in preventing ulcerative dermatitis syndrome. OBJECTIVES: We conducted this work to asses ulcerative dermatitis in C57BL/6 mice colony and reduce it through dietary modification. METHODS: During a two-years period, a C57BL/6 mice colony in a laboratory animal breeding center was monitored for the presence of ulcerative dermatitis syndrome. In the first year, the animals were fed with outbred laboratory mice pellet and in the second year, the modified diet was used based on the nutritional requirements of this inbred mouse. RESULTS: The average numbers of litters per parturition were 3 and 6 in the first year and the second year, respectively. The litter's mortality rate in the first year was 75 % and zero in the second year. The total number of mice remaining in the colony was 220 in the first year, which increased to 1100 in the next year. Syndrome symptoms were observed in the adult mice in the first year. Alopecia was observed mainly in the back and neck and the severity of the symptoms was mild to severe. No mortality was observed in the mice, even in severe cases, and their recovery was spontaneous, yet very slow. In the necropsy, axillary lymphadenopathy, splenomegaly, and hepatomegaly were observed. In histopathological samples taken from the skin lesions, the accumulation of inflammatory cells and the spongiosis of cornea cells were observed. In lymph nodes, spleen, and liver, pathological changes were observed from the accumulation of inflammatory cells to necrosis. In the second year, the number of cases reduced significantly to 2 %. The severity of the symptoms was mild and their recovery was faster than that in the previous year. CONCLUSIONS: By fully supplying the nutritional requirements of C57BL/6 mice, we could significantly prevent the occurrence of ulcerative dermatitis syndrome.