This study was conducted to examine testosterone concentrations its relationship with the scrotal circumference and physical characteristics of semen in aceh bulls. Semen samples were collected weekly from jugular vein of three aceh bulls aged 4-5 years old for 10 weeks. Testosterone concentration was measured by enzyme-linked immunosorbent assay (ELISA) method. Semens were collected by using artificial vagina and evaluated for physical characteristics namely ejaculatory volume, pH, and sperm motility, concentration, and abnormalities. Data were analyzed using correlation-regresion test. Testosterone concentrations showed a positive correlation with scrotal circumference (r = 0.799), number of sperm (r = 0.703), sperm motility (r = 0.857) and sperm abnormalities (r = -0,877). No correlation, however, was found between testosterone concentrations with semen volume (r = 0.038) and pH (r = 0.418). It can be concluded that testosterone concentrations correlated positively with scrotal circumference, numbers of sperm, sperm of motility and sperm of abnormality.