Purpose: to evaluate the biological response of the dog teeth to Platelets Rich plasma (PRP), Platelets Rich fibrin (PRF) and mineral trioxide aggregate (MTA) as pulp capping materials. Material and Methods: A total of 90 teeth of dogs were included. Class V cavities were prepared. Pulp exposure was performed in the middle of cavity floor. The teeth were divided into three groups of 30 teeth according to the material used; A1: PRP, A2: PRF and A3: MTA. Glass ionomer restoration was applied as restoration for the cavities. The tissue response to the materials was assessed at three different post-operative periods of 7, 30, 60 days. The animal was sacrificed. Histomorphometric analysis was performed. Result: the results showed high inflammatory cells count at 7 days for all treated groups; PRP treated teeth showed the highest at 7 days, while PRF showed the least. At 1 and 2 months postoperatively no significant difference was found between all the treated groups. For dentin bridge scores; there was no significant difference between all the materials at 7 days and 1 month. At 2 months; the MTA treated teeth recorded the greatest dentin bridge score as compared to all treated teeth.As for integrity of odontoblast score; results showed no significant difference between different materials at 7 days and 1 month. The MTA treated teeth showed the highest score as compared to PRP and PRF at 2 months. Conclusion: Among the three different materials, PRP and PRF appeared to be promising pulp capping agents.