This work was done to investigate the influence of fiber particle size through physically effective neutral detergent fiber (peNDF) of mixed ration on feed intake, nutrients digestibility, and performance of Egypt ianbuffalo (Bubalusbubalis) heifers. Fifteen animals within experiment were divided into 3 groups (5 per each). Buffalo heifers were allotted to one of variant three diets; G1 (high peNDF content), G2 (moderate content), then G3 (low content), where we made them by mixing feed at variable times (5, 15, and 25 minutes). By multiplying aportion of TMR remainon a 1.18 mm-sieve screen of standard Penn State Particle Separator by NDF portion, we could determine peNDF contents, where they were 29.84%, 28.59%, and 26.59% for the G1, G2, and G3 TMRs, respectively. Feed intake amount was constant with different peNDF amount in TMRs. The better body weight gain observed with G1 group than in G2 and G3 groups (p<0.05), where both groups did not differ. The feed efficiency has a negative relation with peNDF content (G1: 6.4, G2: 7.35, and G3: 9.48 kg/kg), while peNDF content of rations has a linear relation with digestibility of ration nutrients, besides chewing time(p<0.05). Finally, we could conclude that the peNDF amount of ration should be taken in consideration to improve animal performance, feed utilization, and general health in buffalo heifers.