Four Thai-indigenous heifers, average 132±11.71 kg of body weight, were used to determine effect of dietary protein levels on nutrient digestibility and nitrogen utilization using a 4x4 Latin square design with 21d period. Heifers were fed diet containing 6, 9, 12 and 15% of CP. The findings revealed that dietary protein levels did not significantly alter (p>0.05) DM, NDF and ADF digestibilities in heifers. However, CP digestibility of heifers markedly increased (p<0.05) with increasing dietary protein levels. N intake, N fecal and urinary N excretion, N digestion and N retention significantly increased (p<0.05) when dietary protein levels increased. N retentions of heifers fed diet containing 6, 9, 12 and 15% CP were 11.53, 18.64, 24.20 and 31.08 g day^-1, respectively. Based on the results, it could be concluded that dietary protein influenced significantly (p<0.05) CP digestibility and N utilization in Thai-indigenous heifers. Furthermore, the results demonstrated that protein requirement for maintenance of Thai-indigenous heifers was lower than 6% of dietary CP. © Medwell Journals, 2009.