Pain is a major risk factor of post-operative cognitive dysfunction (POCD) in aged population. We investigated the effects of thalidomide, an anti-inflammatory and analgesic drug, on POCD in aged rats, and also explored the underlying mechanisms. Laparotomy was performed under anesthesia in aged rats (24–25 months) to establish POCD models. Thalidomide (5–50mg/kg) was intraperitoneally administered immediately after laparotomy. Within 12h after the operation, pain symptoms were assessed by rat grimace scale (RGS). Within postoperative day (POD) 3–14, spatial memory was evaluated using performance errors in a radial arm maze. Protein levels of inflammatory cytokines and N-methyl-D-aspartate (NMDA) receptors were measured on POD 14. POCD rats treated with thalidomide showed decreased RGS and performance errors, compared with saline-treated POCD rats. Single administration of thalidomide significantly reduced production of cytokines (tumor necrosis factor (TNF)-α and interleukin (IL)-1β) in serum but not in the brain, and attenuated upregulation of NMDA receptor (NR) 2A/B subunits in the hippocampus at POD 14. MK-801 abolished thalidomide-induced attenuation of spatial memory deficits. Our results support that thalidomide could disrupt the development of post-operative memory deficit in aged rats through its long-term regulation of NMDA receptors (NRs) in the hippocampus. Therefore, thalidomide might provide a new means to prevent the development of POCD.