Head and neck cancer is commonly treated with surgery, chemotherapy, radiotherapy either alone or in combination. The purpose of this study is to evaluate the efficiency of fish oil (FO) to preserve periodontal ligament and mandible in gamma irradiated albino rats treated with cisplatin (CP). Thirty male Albino rats were randomly divided into five groups; group C; served as control, group CP; rats were given a single dose of CP (10 mg/ kg body weight i.p), group R; rats were exposed to a single dose of 0.7 Gy γ-rays, group CP + R; rats were given CP and after 24 hours exposed to γ-rays, and group FO+ CP + R; similar to the previous group except for administration of FO (2 ml/ kg body weight) orally and daily for 12 consecutive days before CP injection. The mandibles were collected one day post irradiation and stained with hematoxylin and eosin for histological and histomorphometric analysis. CP and radiation alone or in combination induced bone resorption, degeneration of periodontal ligament fibers. Histomorphometric analysis revealed significant decrease of osteocyte number, fibroblastic and collagen area % and increase of periodontal ligament width. FO protected group showed normal histological appearance of both periodontal ligament and bone. In addition, histomorphometric data revealed normal values of all studied parameters. CP and/ or gamma radiation damage alveolar process and periodontal ligament probably due to osteocyte apoptosis, and supplementary treatment with FO may be potentially useful in protecting alveolar process and periodontal ligament during combined CP chemotherapy and radiotherapy.