Objective: To evaluate the use of platelet-rich fibrin (PRF) in the regenerative therapy of immature canine permanent teeth. Methods: Eight immature premolars of beagle dogs were pulp extracted and cleaned with irrigation, then divided into two groups of empty root canals and those filled with a PRF clot. All of the eight premolars were sealed with mineral trioxide aggregate and glass ionomer cement. Two premolars were left naturally grown as a positive control. The root development was assessed radiographically and histologically after 12 weeks. Results: The radiological findings showed greater increases in the thickness of lateral dentinal wall in the PRF group than in the vacant group. Histologically, dental-associated mineral tissue, connective tissue, and bone-like mineral tissue grew into the root canals independent of PRF clot use. The PRF was able to increase the thickness of dental-associated mineral tissue. However, the vital tissue differed from the pulp dentin complex. Conclusion: Our study demonstrated the feasibility of using PRF-mediated regenerative therapy in pulpless immature teeth for improving tissue repair. Keywords: histological results, immature canine teeth, platelet-rich fibrin, pulp repair