Objective: To determine the effect of orthodontic tooth movement on the expression of interleukin-1β mRNA in rats using RT-PCR. Materials and Methods: Sample consisted of eighteen 8-week-old male Wistar rats. The right maxillary first molar of each animal was protracted using an orthodontic protraction appliance. The left maxillary first molar received no treatment and was assigned as the control group. On day 21, all rats were sacrifice and divided in two equal groups. The first group, group (A), was histologically evaluated for the presence and size of potential resorptive lacunae. The second group, group (B), was investigated using RT-PCR in order to determine IL-1β mRNA expression. Results: Measurements revealed that the mean tooth movement was 0.23 mm in group A and 0.24 mm in group B. The mean depth of the resorptive lacunae was 0.17×10-11 mm2 in the control group and 4.9×10-11 mm2 in the intervention group (control group: left maxillary first molars; right maxillary first molars were divided to group A & B, histologic study of group A assures the existence of resorptive lacunae and its extent relative to control group). The difference between the two groups was statistically significant (p<0.05). The RT-PCR evaluation showed no significant differences in IL-1β mRNA expressions of resorptive lacunae between the treated and untreated groups. Conclusion: Although interleukin1-beta is the most potent stimulator of bone resorption and mediator of inflammatory response, the present study showed that the IL-1beta mRNA was not expressed more significantly in root resorption lacunae of the treated molars relative to the control group.