An in vitro experiment was conducted to study the effect of supplementation of different levels of niacin (0, 300, 400, 500, 600,

700 and 800 ppm) on rumen fermentation and digestibility. The substrate comprised of concentrate mixture, maize fodder and wheat straw (40:20:40). Results revealed that TCA-ppt. N (mg/100 ml incubation media) and TVFA concentration (meq/100 ml incubation media) were signifi cantly (P<0.05) higher at 600 ppm (17.56; 7.28) as compared to control (12.12; 6.38). The molar proportion of propionate was also higher at 600 ppm (26.52%) as compared to control (25.87%). The total gas (ml) production increased in a linear fashion whereas methane level decreased signifi cantly (P<0.05) with graded levels of niacin. The NH3-N (mg/100 ml incubation media) decreased signifi cantly (P<0.05) from 15.26 (control) to 10.71 (600 ppm). The IVDMD (%) and IVOMD (%) also increased from 44.04 to 48.04 and 53.91 to 57.38, at 0 and 600 ppm niacin supplementation, respectively. The three higher levels of niacin viz. 600, 700 and 800 ppm had comparable fermentation parameters viz. digestibility, total gas, methane, TCA-ppt. N, TVFA, acetate, propionate and butyrate. It was concluded that 600 ppm niacin level is comparatively better than other niacin levels