To study the neuropathic pain mechanism, various behavioral responses of animals in to different neuropathic models were considered. Adult male Sprague-Dawley rats weighing 230-280 g were used. Anesthesia was initially induced with pentobarbital I.P. (50 mg/kg). These models included (1): chronic constriction injury (CCI) by loose ligation of the sciatic nerve (2) Spared nerve injury (SNI) by a lesion of two of the three terminal branches of the sciatic nerve. The animals were tested for behavioral responses, thermal and mechanical allodynia and hyperalgesia at 1, 2, 3, and 4 weeks after nerve injury. On day 7: mechanical allodynia was significantly increased in CCI group compared with SNI group. On day 14: mechanical and thermal hyperalgesia were not significantly different in CCI group compared with SNI group. On day 21: mechanical and thermal allodynia and hyperalgesia did not significantly differ in CCI and SNI groups. On day 28: a significant difference was seen between mechanical hyperalgesia and heat allodynia between CCI and SNI groups. The results of the present study demonstrated that both neuropathic models, CCI and SNI produce disturbance of sensory nerves after 2 days and reach to a maximum within 13-14 days. The mechanical sensitivity and thermal responsiveness also increased in ipsilateral limb.