Background: The relation between orthodontic force application and dental pulp tissue has been the subject of studies in the recent years. The present study was conducted to evaluate effect of orthodontic forces on pulp tissues. Materials & Methods: 50 patients required maxillary first premolar extraction for orthodontic treatment were included in the study. A cantilever spring made of 16 × 22 steel wire was used to apply intrusive force to upper first premolars (Group I) and the opposing teeth were considered as control group (Group II). Histologic changes were compared between the control and intrusive groups after 7 days and 1 month. Results: Inflammation at 7 days in group I was none seen in 70% and mild in 30% and in group II was none seen in 80% and mild in 20%. At 1 month was none seen in 100% in both groups. Fibrous tissue at 7 days was none seen in 100% teeth in both groups and at 1 month was none seen in 38% in group I and 100% in group II and mild in 62% in group II. Vascular dilatation at 7 days was none seen in 62% and moderate in 38% in group I and none in 60% and moderate in 40% in group II. Vascular dilatation at 1 month was none in 60% and mild in 40% in both groups. The difference was significant (P< 0.05). Conclusion: There was no obvious histologic changes in pup resulted from mild intrusive force in both groups.