Abstract: This study was to investigate the difference in muscle fiber characteristics of Longissimus dorsi (LD) , Biceps femoris (BF) and Triceps brachii (TB) muscles obtained from Sunit sheep at 5, 6 and 8 months of age, respectively. The aim of study was to obtain theoretical knowledge through regulating the muscle fiber type transformation so as to improve the meat quality. The variety muscle fiber types were classified by histochemical analysis of the myosin ATPase method with an acid preincubation solution (pH4.6) . The results showed that fiber number percentage of type Ⅱ B was most common in three anatomical locations. Fiber number percentage of typeⅠin TB and BF were significantly higher than that in LD (p<0.05) . The area percentage of type Ⅰ, fiber number and area percentages of type ⅡA, the diameter and cross-sectional area of type ⅡA and ⅡB in TB were significantly higher than that in BF (p<0.05) , that in BF were significantly higher than in LD (p<0.05) .Fiber number percentage of type Ⅰ in LD of 5 months of age was significantly higher than that of 6 and 8months of age ( p < 0. 05) , however, fiber number percentage of type Ⅱ A in LD of 8 months of age was significantly higher than that of 5 and 6 months of age (p<0.05) . The diameter of type Ⅰ, fiber area percentage and diameter and cross-sectional of type ⅡA of 5 months of age were significantly lower than that of 6 and 8months of age (p<0.05) .