Objective- To investigate the effect of intratendinous injection of bMSCs on the rate and extent of tendon healing after primary repair in a rabbit model. Design- Experimental study. Animals- Twenty seven skeletally mature New Zealand white rabbits weighing 1.8- 2.5 kg were used. Twenty rabbits were used as the experimental animals, and seven others were used as a source of bone marrow-derived mesenchymal stem cells. Procedures- Under general anesthesia an experimental tenotomy was made through the midsubstance of the DDF tendon .The transected tendon was immediately repaired with use of a locking-loop suture. No treatment was given to control group (n = 10). Rabbits in treatment group (n = 10) were subjected to receive bone marrow-derived mesenchymal stem cells. Operated limbs were immobilized for two weeks post operatively. Samples from operated tendons were harvested at weeks of three and eight of operationfor histopathlogicalevaluation , which included evaluation of quantitative and qualitative assessment (twenty specimens). Results- Histological findings revealed that there were significant improvements in structural characteristics of granulation tissue.Neovascularization and cellular proliferation also increased at the synovial layer of the epitenon (increased thickness)in the bone marrow-derived mesenchymal stem cells intreatment group compared to the control group at the week three (P<0.05). At the week eight there were no differences between the groups with regard to histologic characteristics (P>0.05). Conclusion and Clinical Relevance- Intratendinous application of bone marrow-derived mesenchymal stem cells following primary tendon repair can significantly improve the histologicalparameters in the early stage of tendon healing. Early timeperiod during tendonhealing is crucial in the treatment of tendon injuries.