Abstract: Objective: To investigate the expression and changes of sphingosine-1-phosphate receptor 2(S1PR2)in chronic apical periodontitis of rats.Methods: 20 SD rats were selected, and 4 rats were sacrificed randomly as observation objects on 0 day.The model of apical periodontitis was established in the mandibular first molars of the other rats, and 4 rats were sacrificed randomly on day 7, 14, 21 and 28.HE staining and tartrate-resistant acid phosphatase(TRAP)were used to detect osteoclasts.The expressions of S1PR2, receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) were detected by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR).Results: HE staining showed that no obvious abnormality was observed in root tips on day 0.A small amount of inflammatory cells infiltrated on day 7 and increased on day 14; osteolysis increased on day 21; inflammatory cell infiltration was obvious on day 28.RT-qPCR results showed that the mRNA expression of S1PR2 increased gradually from 0 d to 28 d, and was higher on day 7, 14, 21 and 28 than that on day 0 (P＜0.05).The expression of RANKL increased gradually from 0 to 21 d, reached its peak on day 21, decreased on day 28, and was higher on day 7, 14, 21 and 28 than that on day 0(P＜0.05).The expression of OPG decreased gradually from 0 d to 14 d, reached the lowest value on day 14, increased from 14 d to 28 d, and was higher on day 0, 7 and 28 than that on day 14 (P＜0.05).TRAP stainning results showed that the expression trend of osteoclasts and RANKL was consistent. S1PR2 was positively correlated with the expression of RANKL and osteoclast number (P＜0.05), while RANKL expression was negatively correlated with OPG expression (P＜0.05).Conclusion: S1PR2 mRNA expression increases with the development of apical periodontitis, suggesting that S1PR2 may be involved in the occurrence and development of chronic apical periodontitis.