Ossifying fibroma is a type of fibro-osseous lesion categorised into cemento-ossifying fibroma and juvenile ossifying fibroma. Malignant transformation of fibro-osseous lesions is documented especially for fibrous dysplasia, but scarcity is seen when we search for malignant transformation of ossifying fibroma. Thus, we are presenting an extremely rare case of cemento-ossifying fibroma transforming into osteosarcoma with long sequential radiographic details.