Objective To evaluate the change in the expression of ATP-sensitive potassium (KATP) channels in spinal dorsal horn neurons in rats with chronic post-thoracotomy pain (CPTP). Methods Twenty male SD rats, weighing 250-350 g, were randomly divided into 2 groups ( n = 10 each): sham operation group and CPTP group. The animals were anesthetized with 10% chloral hydrate 300 mg/kg, tracheostomized and mechanically ventilated. At 1 d before operation, and at 1, 5, 10, 15, 20, 25 and 30 d after operation, paw withdrawal threshold to yon Frey filament stimulation was measured and the acetone test was performed. The responses of the hindpaw to the acetone test within 1 min were recorded. The rats were sacrificed at 30 d after operation, and the cervical and upper thoracic segments of the spinal cord were removed to detect the expression of KATP channels in spinal dorsal horn neurons by immuno-histochemistry. Results Compared with sham operation group, mechanical pain threshold was significantly decreased at 5-30 d after operation, the response frequency was significantly increased at 20-30 d after operstion, and the expression of KATP channels in spinal dorsal horn neurons in the thoracic segments was down-regulsted at 30 d after operation in CPTP group ( P ＜ 0.05). Conclusion The expression of KATP channels in spinal dorsal horn neurons is down-regulated in rots with CPTP,which may be involved in the pathophsiology mechanism of CPTP.