Purpose: Opioid tolerance remains a challenging problem, which limits prolonged drug usage in clinics. Previous studies have shown a fundamental role of platelet-derived growth factor receptor beta submit (PDGFR beta) in morphine tolerance. The aim of this study was to investigate the mechanisms of spinal PDGFR beta activation in morphine tolerance. Methods: Rats were treated with morphine for 7 days and the effect of drug was evaluated by tail-flick latency test. By using Western blot and real-time PCR, the interaction between mu opioid receptor (MOR) and PDGFR beta in microglia activation, as well as related signaling pathways during morphine tolerance were investigated. Results: Chronic PDGFR beta agonist could induce microglia activation in spinal cord and decrease the analgesic effect of morphine. PDGFR beta inhibitor suppressed microglia activation during the development of morphine tolerance. Furthermore, antagonizing MOR could effectively inhibit the phosphorylations of PDGFR beta and JNK. Blocking PDGFR beta had no influence on JNK signaling, while JNK inhibitor could decrease the phosphorylation of PDGFR beta. Conclusion: These results provide direct evidence that repeatedly activating MOR by morphine could induce the transactivation of PDGFR beta via JNK MAPK in spinal cord, which leads to microglia activation during the development of morphine tolerance.