Abstract: In order to investigate the morphometric changes of tendons of rats at different grow-ing ages,the tendons of extensor digitorum longus to the middle toes from 0，6 and 12-week-old female Wistar rats were taken for microscopic observation and morphometric analysis. The results showed that with the increase of the age,the tendon blast cells decreased and become slender,collagens increased and become more regular in arrangement,and the diameter of tendons become larger, from 13.1±2.2nm at 0-week-lod to 135.0±21.3nm at 12-week-old. It was concluded that there are marked differences on the morphometry of rat tendons at different growing ages.

Key words: Tendon, Rat, Collagen fibril, Age