An experiment was conducted to determine the effect of cotton seed cake inclusion on testicular histometry of red sokoto bucks. Sixteen sexually matured Red Sokoto bucks were randomly allotted to four dietary treatments wit four animals per treatment. Treatment compared were T1 = 0% cotton seed cake (CSC), T2 = 10% CSC, T 3 = 20% and T4 = 30% CSC respectively. The results of chemical composition show that the crude protein (CP) content was generally high for all the diets. The ash, ether extract (EE), neutral detergent fibre (NDF) and gross energy values (GE) were all highest in T 3. The gonadal sperm reserve (x106) reveals the right and left testis to be significantly higher (p<0.05) in T1 than the other treatment groups (2762.6 x 106) and (2761 x 106). The result of the extra gonadal sperm reserve showed significant difference (p<0.05) in all the parameters observed except for left caput epididymides and right caudal epididymides. The result of testicular morphometry showed significant effect (p<0.05) in all the parameters observed. The result also shows histological changes at higher level (30% CSC inclusion). Base on these findings, 10 and 20% level of CSC inclusion does not have any negative effect on testicular morphometry of Red Sokoto buck as reveal by the photomicrograph section of the testis.