Objective To observe the expression of potassium-chloride co-transporter(KCC2) in spinal cord dorsal horn in nicotine withdrawal rat. Methods Sixty adult male SD rat, weighing 180-250g,were randomly divided into 3 groups using a random number table, including control group(C group,n=12) ,normal saline group (NS group,n=12),nicotine withdrawal group(NT group,n=36) ,received no injection, subcutaneous injection of normal saline, nicotine 3 mg/kg respectively three time a day for seven days. At 60 min after the last injection of nicotine, subcutaneous injection of mecamylamine 1 mg/kg was given for each rat. We observe thermal withdrawal latency (TWL) after nicotine withdraw and the expression of the potassium chloride cotransporter 2(KCC2) in spinal cord dorsal horn. The distribution and expression of KCC2 in the spinal cord dorsal horn(L4-5)was determined by Immunofluorescence and Western blotting analysis respectively. Results Compared with Control group and NS group, there is no difference in TWL[（16.13±0.25）s vs（15.52±0.20）s] (P>0.05); Compared with NT group, TWL decreased significantly after nicotine withdrawal[（16.13±0.25）s vs（10.50±1.43）s] (P<0.01),especially in the fourth day after the nicotine withdrawal was reduced to a minimum.The expression of KCC2 was significantly lower in NT group than in the other groups[（16.13±0.25）s vs（8.4±0.3）s] (P<0.01),but there was no difference in other groups[（1.04±0.02）vs（0.23±0.01）] (P>0.05). Conclusin Nicotine withdrawal can suppress the expression of KCC2 in spinal cord dorsal horn in rat.