A total number of twenty two male lambs, nine of Chios and thirteen of Rahmani ram lambs, were used  to investigate the effects of body weight of lambs, type of birth, weight at birth, weaning system and age at puberty on the development of the six testicular parameters from weaning 8-16 weeks of age in both Chios and Rahmani ram lambs        Lambswere assigned randomly at birth to three groups: 1) Lambs were weaned at 8 weeks of age (early weaning); or 2) Lambs were weaned at 12 weeks of age (normal weaning); or 3) Lambs were weaned at 16 weeks of age (late weaning). Results revealed that, no significant differences were observed between breed on birth body weight of lambs. However, at 90,180 and 360 days of age, Chios lambs were significantly (P<0.01) heavier than Rahmani lambs. Weaning weight was reduced at 90 days, but there was a quick recovery to similar weight by yearling age. Age at puberty in ram lambs was significantly affected (P < 0.01) by weaning system. Puberty occurred earlier in early weaning (8 weeks) (279 d) and normal weaning (12 weeks) (255 d) compared with late weaning (16 weeks) (313 d). Breed was significantly differences of testicular measurements. Types of birth were not significantly affected the development of testicular parameters. Increasing of testicular parameters were relatively similar to the development of body weight. In general, sexual development of ram lamb appears to be more closely associated with body growth. Measurement of testis were positively correlated with body weight (r= 0.60 - 0.85, P<0.01) and each other testicular parameters (r= 0.50 - 0.69, P <0.05, P<0.01).