Trigonelline (TRG) and nicotinic acid (NA), in which the former but not the latter improved the blood glucose level in the oral glucose tolerance test (OGTT) in Goto-Kakizaki (GK) rats were tested for anti-diabetic effects in mellitus models of KK-Ay obese mice that had type 2 diabetes. Blood glucose level in OGTT carried out on day 22-23 was lowered after feeding in mice fed TRG and NA than that of the control mice not fed these compounds, indicating that both TRG and NA have sufficient activity to improve glucose tolerance in diabetes with obesity. The serum insulin levels at fasting showed significantly lower levels in mice fed TRG, and a lower tendency in mice fed NA, compared with the control mice. The triglyceride (TG) levels in the liver and adipose tissue in mice fed TRG and NA showed lower values or a lower tendency than those of the control mice, indicating that TRG and NA were also effective to improve the changes in lipid levels accompanied with diabetes. Higher values or a higher tendency of the glucokinase (GLK) / glucose-6-phosphatase (G6Pase) ratio in the liver and lower levels of the serum tumor necrosis factor (TNF) -α in the TRG- and NA-fed mice, compared to the control mice, suggested that the regulation of GLK and G6Pase, and TNF-α production by TRG and NA are closely related in suppressing the progression of diabetes in the KK-Ay mice.