In order to investigate the effects of physical form of starter diets and hay contents on the expression of insulin like growth factor 1 and 2 (IGF-1 and IGF-2) in rumen of Holstein dairy calves, 52 calves (male) were used in a completely randomized design. Dietary treatments were: 1) ground (G), 2) texturized (steam flake corn and steam flake barley), (T), 3) pellet (P) and 4) ground+10 % forage (GF). All calves were weaned at d 50. Diets were formulated to be isoenergetic and isonitrogenous. At d 70, 12 calves were randomly selected and slaughtered. Gastrointestinal tract was removed and the tissue samples from cranial ventral sac of rumen were collected, and then snap frozen in liquid nitrogen, and stored at ?80 ° C. After RNA extraction and construction of cDNA, the Real Time PCR method was used, and gene expression levels were studied. The ?-actin gene was used as housekeeping gene. Expression of IGF-1 was influenced by physical shape of diets (P 0.001). The highest expression of IGF-1 was observed for calves used P, T, G and GF respectively. However, expression of IGF-2, was not influenced by the treatments (P = 0.21). Results show that coefficient of correlation between IGF-1 and IGF-2 was positive but not significant (P = 0.15). The correlation between IGF-1 gene expression and histological parameters of the rumen for length of villi and keratinocyte layer were significant (-0.72 and 0.73 respectively) at P 0.03. The correlation between the expression of IGF-2 and histological parameters of the rumen was not significant. The resultsin this study showed that the physical form of starter could affected the expression of IGF-1 and more expression was observed in P and T. Perhaps because rumen environment is more acidic in P and T compared to GF diet. Key Words: Holstein Calf, Starter diets, Forage, Insolin like growth factor, IGF-1, IGF-2.