Vitamin A is one of the fat-soluble vitamins. Because of its particular role in different tissues and organs, various clinical signs are seen in deficiency conditions. In addition, sometimes marginal deficiency is present without obvious clinical signs but performance defects, such as infertility is seen. In present study seasonal changes of serum vitamin A in 22 Arab horses was investigated in Ahvaz. A simple and cheap method (spectrophotometrye) was used for measuring vitamin A. The results were analyzed statistically by one- way analysis of variance (ANOVA). The results indicated that mean vitamin A values (20.37±1/21mg/dl) were within normal range. The values of vitamin A in different seasons and two sexes were normal, too. Serum vitamin A value in spring was significantly higher than other seasons.