The objective of this research was to determine the effect of dietary crude protein levels on nutrient digestibility, ruminal fermentation and growth rate in Thai-indigenous yearling heifers. Sixteen Thai-indigenous yearling heifers, with an average initial body weight of 118±15.39 kg were assigned to one of 4 treatments according to a completely randomized design. Dietary treatments contained 4 levels of crude protein (6, 8, 10 and 12%). Diets were fed at the rate of 3% BW. The findings revealed that dietary crude protein levels did not significantly alter (p>0.05) DM and OM digestibility in yearling heifers. However, CP, NDF and ADF digestibility of heifers increased (p<0.01) with increasing dietary crude protein levels. Ammonia nitrogen, blood urea nitrogen and average daily gain linearly increased (p<0.01) with increasing dietary protein. Base on the results, it can be concluded that increases dietary crude protein level did improve nutrient digestibility, ruminal fermentation and growth rate of Thai-indigenous yearling heifers. Additionally, it has been suggested that level of dietary crude protein should be higher than 12% during accelerated Thai-indigenous yearling heifer growth periods.