In this study, the effects of age on body measurements that obtained from different horse age groups were researched by orthogonal polynomials methods. In the results of orthogonal comparison, linear, quadratic and cubic effects were found to be statistically significant for height at withers, height rump and chest width (p<0.01) and (p<0.05). Linear and quadratic effects were found to be statistically significant for body length, chest girth, chest depth, rump width, tail length, front shank length and head length (p<0.01). Linear and cubic effects were found statistically significant for leg length (p<0.01 and p<0.05). Linear effect was found statistically significant for ear length (p<0.01). Variation in body size can be explained by at most linear effect. As a result, linear effect adequated impact of age on body measurements in horses when working with orthogonal polynomials. Furthermore, the effect of age on the ear length is linear. The effect of age on the body length, chest girth, chest depth, rump width, tail length, head circumference and length effect is quadratic. The effect of age on the withers height, rump height chest width and leg length is cubic