An experiment was conducted to study the effect of dietary concentrate level in cattle on rumen fermentation characteristics, its enzyme profile and ciliate protozoal population. Twelve rumen fistulated adult cattle were divided into two equal groups (group C30 and C60). The concentrate fed to group C30 and C60 contained 32 and 16% crude protein (CP) while the concentrate roughage ratio in the diet was 30:70 and 60:40, respectively. Daily dry matter intake was higher (P<0.01) in group C60 than in group C30 amounting to 2.31 and 2.06% of body weight, respectively. The rumen fluid volume and its fluid flow rate were higher (P<0.01) in group C30 than in group C60. The pH of strained rumen liquor (SRL) was lower (P<0.01) in group C60 while total volatile fatty acids (TVFA) concentration was higher (P<0.01) in group C60 than in group C30. The ruminal concentration of total nitrogen, NH₃-N and trichloroacetic acid precipitable nitrogen (TCA-ppt.-N) were also higher (P<0.01) in group C60 than in group C30. The activities of carboxymethyl cellulase (CMC-ase) and xylanase in the rumen of group C30 was significantly (P<0.01) higher than in group C60 while the activities of amylase and protease enzymes were higher (P<0.01) in SRL of group C60. The activities of (3-glucosidase and urease were not affected by level of concentrate feeding. The total number of rumen ciliate protozoa was higher (P<0.01) in group C60 (37.2 x 10⁴/ml SRL) than in group C30 (30.1 x 10⁴/ml SRL). The rumen protozoa of both groups were B-type population. The numbers of holotrich protozoa in the rumen of group C30 and group C60 were 1.4 x 10⁴ and 2.1 x 10⁴ whereas the numbers of entodiniomorphid protozoa were 28.7 x 10⁴ and 35.2 x 10⁴ per ml SRL, respectively. It was concluded that TVFA production as well as total nitrogen concentration and their fractionations were higher in the rumen of high concentrate fed animals. The total and differential protozoal counts were also higher in high concentrate fed groups, due to a higher availability of dietary starch. Additionally it was evident that the activities of polysaccharide-degrading enzymes depend on their respective substrate concentration in the rumen.