This study was conducted to investigate the effect of thyroglobulin (TG) treatments on growth rate, some testicular measurements, semen characteristics and blood constituents. Fifteen buffalo bulls aged 21 - 28 months with average initial body weight 305.8 ± 2.5 kg. were divided randomly into three comparable groups (5 animals in each) and subjected to one of the following treatments throughout 24 weeks: The first group (C ) : served as a control group without any treatment. Bulls of the second group (TG1), were subjected to ration administration of thyroglobulin treatment (high content of potassium iodide, 1gm. plus 0.25 g iodine) at the rate of 50 ml/head twicea week. Bulls of the third group (TG2), were subjected to ration administration of thyroglobulin treatment (low content of potassium iodide, 0.6 gm. plus 0.25 g iodine) at the rate of 50 ml/head twice a week. Differences in live body weight (LBW) between treated groups and group C were highly significant (P < 0.01). The treated group TG1 attained 17.75% higher LBW than that of group C and showed a significant increase indaily weight gain (DWG) as compared with other groups. Concentrations of blood total proteins or its fractions (albumin and globulin) were significantly (P <0.05) the highest in group TG1 when compared with those of groups C and TG2. Concentrations of glucose and blood urea nitrogen (BUN) were significantly different between groups (P < 0.05). Group TG1 had significantly (P < 0.05) higher content of cholesterol and creatine in blood as compared with other groups. Group C showed the least content of creatinine whereas TG1 had the highest content among treated groups. Group TG1 showed significantly (P < 0.05) greater transaminases activity (ALT and AST) than that of all other groups. Concentrations of T4 increased to 9.87 µg/dl at the 3^rd phase of growth in TG1 group. Similar trend was observed for testosterone concentration. Scrotal circumference was greater in TG treated groups than that of group C by reaching the 3^rd stage of growth. Higher testicular volume was observed for the treated TG1 group by 22.97% over that of group C at the 3^rd stage of growth. The least values of semen volume were obtained by group C throughout growth stages whereas the maximum volumes were achieved by groups TG1and TG2. Higher libido (less reaction) was exhibited by groups TG1 as compared with groups TG2 and group C. Group TG1 showed the maximum sperm concentration as compared with other groups. Groups TG1 and TG2 achieved higher sperm output by 27.43% and 4.36% than group C at the 3^rd stage of growth. Differences in sperm abnormality between groups were significant (P < 0.05) where the minimum percent was that of TG1 (15.38%). The highest percentage of live sperms was attained by group TG1 (72.1 %) at 3^rd stage of growth. It can be concluded that higher dose of thyroglobulin (1gm.of potassium iodide plus 0.25 g iodine) at the rate of 50 ml/head twice a week, had promoted growth of buffalo bulls, enhanced its metabolic activity hence improved male libido, output of semen and its physical characteristics.