Introduction: The purpose of this study was to investigate the effect of psychological stress on orthodontic tooth movement in Wistar rats. Materials and methods: Forty-eight female ten-week old Wistar rats with an average weight of 188 ±12 gr were selected and randomly divided into two experimental and control groups. The experimental group received crowded environment-induced and cat odour stresses 4 weeks before spring insertion. On the 29th day in both groups, maxillary incisors were moved by the insertion of springs and exactly after 7 days, 9 rats from each group and after 14 days the remaining rats were sacrificed. Then the mesioincisal distance between maxillary incisors was measured. Afterwards, histological sections were prepared to count osteoclasts under a light microscope. The data on the extent of orthodontic tooth movement and the number of osteoclasts were analyzed by independent sample t-test. Results: The results indicated that on the 7th day after spring placement the orthodontic tooth movement was significantly higher in the control group compared to the experimental group (p<0.05). The number of osteoclasts at a significance level of ?=0.1 in the control group was higher compared to the experimental group. On the 14th day after spring placement, the orthodontic tooth movement in the control group was significantly higher compared to the experimental group (p<0.05). However, there were no significant differences in the number of osteoclasts between the two groups. The rats experienced weight loss in the experimental group (p<0.05). Conclusions: Psychological stress led to a decrease in orthodontic tooth movement and in the number of osteoclasts around the root in the movement direction in rats, but a decrease in osteoclast counts was not parallel with time and demonstrated a nonlinear pattern. In addition, psychological stress led to weight loss in rats.