Damage on one side of the body evoked pain bilaterally on both the injured and uninjured sides. The abnormal phenomenon called mirror image pain, is generally observed in many clinical pain syndromes and in various animal pain models. However, its mechanism is not fully understood. In the present study, we investigated the mechanism of mirror image pain in the complete Freund's adjuvant (CFA)-induced inflammatory pain model measuring the revealed mechanical allodynia by von Frey filament test. After CFA injection, the paw withdrawal threshold to mechanical stimuli was significantly decreased not only in the ipsilateral paw (CFA injected paw) but also in the contralateral paw (CFA non-injected paw). The decrease in mechanical threshold of the contralateral paw, which is called mirror image pain, had delayed onset as compared to the ipsilateral mechanical allodynia. NMDA receptor antagonist treated after CFA injection did not attenuate bilaterally allodynia, however, pretreatment with NMDA receptor antagonist was significantly attenuated the development of mirror image pain, without affecting the ipsilateral mechanical allodynia. These results suggest that the mechanism of mirror image pain via NMDA receptor activation was different from ipsilateral mechanical allodynia.