Aim of the study: was to evaluate the effect of nano second pulsed electromagnetic field (PEMF) on osteo-arthritis of tempromandibular joint. Materials and Methods: This study included 30 female rats with induced osteo-arthritis of the tempromandibular, 6 rats of all 30 rats were sacrified to insure of arthritis existence joint. Remained 24 rats were divided into 2 groups the 1st group received no treatment and the 2nd received treatment with PEMF for (4-6-12) days, then all rats were scarified after 20 days to be examined histologically. Results: treatment of early arthritis with PEMF for 12 days showed improvement in the histological features of signs of arthritis.