The data show no effect of the level of FCP on digestibility of nitrogen or on nitrogen retention. Chhay Ty et al (2003) reported that diets based on ensiled cassava leaves had no effect on both nitrogen digestibility and nitrogen retention of growing pigs. In this study, the range of values for retained nitrogen (6.84 to 8.16 g/day) were higher than that in the report of Chhay Ty et al (2003) (range of 4.4 to 5.4 g/day) although nitrogen intake on the ensiled cassava leaf diet (13 to 14.7 g/day) were higher than present diets (12.4 to 13.9 g/day). The data are in agreement with Lizardo and Aumaître (2001) who reported that total tract digestibility of N was not affected when six to twelve percent of beet pulp in piglet diet was used. In addition, a previous study indicated that dietary fermentable fiber did not affect nitrogen retention and reduced urinary urea excretion (Zervas and Zijlstra 2001). In the present study, fecal nitrogen was not different among treatments but urinary nitrogen tended to be reduce as FCP added to the diets. The ammonia emission inside and outside the farm will be reduced with lower urinary nitrogen excretion (Zervas and Zijlstra 2001). The results of this study can contribute a strategy to farm management in reducing nitrogen excretion by diet management.