Aim: The purpose of this study was to investigate the success rate of PDL injection in primary maxillary molars anesthesia. Materials and Methods: This study was performed using a sequential double blind randomized trial design. In this study 82 children aged3–7years old who required pulpotomy, restoration, SSC and extraction on their primary maxillary molars were selected. The teeth of these children were anesthetized with periodontal injection and the dental treatments were performed on each patient. Signs of discomfort, including hand and body tension and eye movement, verbal complaint and crying (SEM scale), were evaluated by a dental assistant who was blinded to the treatment allocation of the patients. Results: Results of this study showed that during treatment 76.09% of child patients had verbal compliant, 4.87% of cases cried and no patient had body and eye movements. The success rate of PDL injection was 92.47%. Conclusion: Results showed that periodontal ligament injection can be used as an alternative to infiltration in maxillary primary molars.