This study was conducted to evaluate the effect of feeding supplemented diets by ether niacin, thiamin or its mixture on the growth and fattening performance of buffalo calves. A feeding trial was carried out using twenty growing buffalo calves with average initial weight 275±2.6 Kg and aged 14 months. They were divided into four similar groups (5 calves each) in 120- day feeding trial periods using the randomized complete block design. All animals' groups were fed individually along the experimental period on a basal ration (BR) that consisted of 69.5% concentrate feed mixture (CFM), 17.4% rice straw (RS) and 13.1% corn silage (CS) on DM basis. A certain amounts of dietary niacin and/or thiamin were mixed thoroughly with CFM as in the following treatments. Animals were given BR without supplements (T1) as control, BR supplemented with 0.5 g niacin/head/day (T2), BR plus 0.5 g thiamin/h/d (T3) and BR supplemented with 0.25 g niacin and 0.25 g thiamin/h/d (T4). Animals were fed according to allowances of kearl (1982) for buffalo calves. Four digestibility trials were conducted to determine the digestibility and feeding values of the experimental rations. Results indicated that digestibility of DM and OM were insignificantly increased with T2 and T3 rations, but significantly (p<0.05) increased with T4 one, compared with control (T1). Digestibility of CF, EE and NFE followed the same trend of DM among treatments. Otherwise, CP digestibility was slightly improved with all tested rations. The values of TDN, DCP and DE were followed similar trends to that of nutrients digestibility among treatments. Daily feed intake wasn't affected significantly by the two supplements. Total weight gain and daily gain were significantly (p<0.05) higher in all tested rations in comparison of control one, while the highest value had occurred with T4. Regarding feed conversion measurement, significant improvement due to both supplements and its mixture were found respecting DM,TDN or DCP: gain, compared with unsupplemented diet (control). Concerning economic evaluation, net revenue and economical efficiency were markedly increased with supplemented rations compared with control one. No significant differences were found among treatments in blood total protein and creatinine. It could be concluded that either niacin or thiamin and its mixture had an effectiveness role for improving the performance of fattening buffalo calves when the concentrate feed mixture was high percentage in their rations.