Fifty broiler chickens of both sexes were used in this study. The chickens were bought at 8 weeks old and kept until 40 weeks old. During this period the development of ossification and mineralization was followed. The chickens were killed at weekly intervals. After having been examined fresh, the tendons were fixed in appropriate fixatives and processed for histological and histochemical examination. The earliest signs of mineralization were noted at 15 weeks and mineralization was apparent on X-ray photographs at 20 weeks. The development of ossification of the tendons has been described. The fibroblasts transformed into osteoblasts which secreted around the cells and later between the fibres. This was followed by the appearance of osteoblasts and resorption cavities and then the latter became lined by osteoblasts, and osteones were formed.