Leptin is widely distributed in many tissues, including the nervous system. However, the ontogeny of leptin expression in the dorsal root ganglion (DRG) is unclear. Recent studies have shown that leptin is involved in the regulation of neuropathic pain induced by nerve injury. Our previous results showed that exogenous leptin administration alleviated the pain behaviors induced by chronic constriction sciatic nerve injury. In the present study, the ontogenic expression of leptin was detected in the DRG of the mouse embryo at days 15.5 (E15.5), E17.5, and E19.5 of gestation and in the postnatal mouse at days 5 (P5), P15, and P25, and in the adult mouse. Leptin immunoreactivity and mRNA were not found in DRG at E15.5. The percentage of leptin immunopositive (leptin) neurons was about 27% at E17.5. It continued to increase to about 70% at P5. From P5 to P15, there was no significant change. The proportion of DRG neurons positive for leptin decreased after P15 and there were about 41% leptin neurons in adults. The expression profile of leptin mRNA is similar to leptin immunoreactivity. Oxaliplatin (OXA) is an effective platinum-based drug used as first-line chemotherapy for advanced colorectal cancer. However, it may induce neuropathic pain. In the current study, we found that the expression of leptin was increased in the lumbar 4-6 DRG of OXA-treated mice. These results indicate that leptin is involved in the regulation of DRG development and OXA-induced neuropathic pain.