Introduction. Oral ulcers are one of the most frequent diseases in the oral cavity. Wound healing is a complicated process including inflammation, proliferation, epithelialization, angiogenesis and collagen matrix formation. The aim of this study was to evaluate the effect of oleuropein upon oral wound healing in healthy and diabetic mice by counting mast cells using toluidine blue staining. Methods and materials. The experimental study was performed on 96 mice divided into 6 groups: the control, the group receiving oleuropein extract, those receiving base material, diabetic control, diabetic receiving oleuropein, and the diabetic group receiving the base substance. 2 mm ulcers were made on the palate of mice and the animals were sacrified on the 2nd, 4th, 6th and 8th day. Blocks prepared from the wound area were stained using standard toluidine blue, and a number of granulated and degranulated mast cells was studied under the optical microscope. Data was entered into a checklist and analyzed using statistical software SPSS 21, ANOVA and Post hoc Tukey tests, at a significant level of 0.05. Results and discussion. In this study, the average of granulated mast cells was significantly lower than degranulated mast cells. There was a significant difference between the average of degranulated mast cells in the diabetic animal using the base and control group. In the test-group DD (diabetics animals having received Oleuropein), on the second day, mast cells were significantly more than in the controlgroupanddiabetic animals which received base substance and the group of healthy animals receiving Oleuropein. Conclusions. The findings of this study showed that the oleuropein extract significantly increased the mast cell count of samples taken from ulcers of diabetic mice.