The effect of GnRH and improved diet was determined on serum testosterone level and scrotal circumference of buffalo bull. Two old age and one young buffalo bulls were used. The study was conducted in three phases. During first month only normal diet was given to all three bulls. In second month additional diet with 14% protein and 50g dicalcium phosphate) was given to all three bulls twice a day and in third month, bulls were fed with green fodder and a ration containing 14% protein. GnRH was given to one old age bull at the start of the month and every week to second old age bull for 4 weeks. Young bull was kept on improved diet during third month and no treatment of GnRH was given. Improved diet did not effect on scrotal circumference of old age bulls but in third month, significant increase in scrotal circumference of young bull occurred. Improved diet raised serum testosterone level as was observed in second old age bull but with improved feed plus GnRH administration to old age bulls increased in scrotal circumference was significantly. This increase was more pronounced in bull which received GnRH injection at weekly interval than the one which received GnRH once a month.