NADPH-Cytochrome p450 oxido-reductase (CPR) plays an important role in the metabolism of a wide range of chemicals and drugs.The purpose of this study was to assess the effect of infertility agents on the expression of CPR in plateau pikas (Ochotona curzoniae) .Food baits (oats,fodder or carrot) containing either quinestrol (E) (10 mg/kg) ,levonorgestrel (P) (10 mg/kg) ,EP-1 (mixture,10 mg/kg) or water (control group) were presented to 4 groups of 10 animals for 28 days.Kidney tissues were collected from the animals at 30 days after the start of baiting.A CPR genomic fragment of 2 038 bp of O.curzoniae was amplified and sequenced (accession No.1021728) .Selective pressure analysis identified the following sites to be under positive selection: 21A,79G,127S,160A,207S,239A,418L,541T,632Q,673S,and 727E.Two-way ANOVA showed that quinestrol did not affected the expression of CPR significantly (F1,29 = 2.695,P = 0.111) ,levonorgestrel affected the expression of CPR significantly (F1,29 = 26.967,P <0.001) ,and there was no significant interaction between levonogestrel and quinestrol (F1,29 = 0.137,P = 0.714) .Our study has shown that in plateau pikas,levonorgestrel significantly depresses the expression of CPR by 43.7% (P<0.01) when compared with the control group.