Abstract: Objective To investigate the effect of intracerebroventricular injection of morphine and Orphanin FQ (OFQ) on somatosensory evoked potential (SEP) and Na+-K+ATPase activity in cerebral cortex of rat. Methods Study the SEP with the BL-420 biological signal collecting system. The cerebral cortex tissues were extracted, homogenized and centrifuged. Na+-K+ATPase activity was measured with ATPase analytical box. Results After intracerebroventricular injection with OFQ 0.9μg, the amplitude of P1-N1 and N1-P2 increased significantly (P<0.01). After intracerebroventricular injection with OFQ (0.04, 0.45, 0.9, 1.8 μg)， the Na+-K+ATPase activities were significantly decreased, with the increase of concentration of OFQ (P<0.01). After intracerebroventricular injection with morphine (20μg), the amplitude of P1-N1 and N1-P2 decreased significantly and the activity of Na+-K+ATPase increased significantly (P<0.01). After intracerebroventricular injection with OFQ (0.9μg) and morphine(20μg), the amplitude of SEP and the Na+-K+ATPase activity were not significantly different as compared with control groups. Conclusion It suggests that the effect of OFQ is related to the changes of the SEP amplitude and the Na+-K+ATPase activity in CNS.