The effect of replacement of maize grain by animal fat in a diet with high level of acid detergent fibre (27%) on diet digestibility, rumen fermentation and energy content of the diet was evaluated. Six fistulated wether sheep were used in a 2 x 2 Latin square experimental design in three replicates. Forage : concentrate ratio in the diets was 47.7 : 52.3 and animal fat contributed to concentrates by 7%, replacing maize on a weight basis. Digestibility of ether extract was increased (P<0.001) by 13.1% for the diet with fat compared to the diet without fat, while digestibility coefficients of the other nutrients were unaffected. The energy content of the diet with fat increased by 3.4% (P<0.05). The inclusion of animal fat to sheep diet increased significantly the molar proportion of propionate (P<0.05) by 10.7% and the crude protein degradability (P<0.001) by 4%, and decreased the molar proportion of butyrate by 6.1% (P<0.05), the acetate to propionate ratio (P<0.01) by 13.2%, and the protozoa counts by 32% (P<0.001). The results showed that animal fat can replace cereal grains in sheep diets up to the level of 5% without any problem on rumen fermentation process.