【Objective】To investigate the effect of letrozole on the reproductive function and linear growth in the early and mid pubertal boys.【Methods】43 early and middle pubertal boy with seriously damaged predict adult height， treated with letrozole 1.5 mg/m 2 /d Po（≯2.5mg/d）were enrolled as treatment group. 48 cases of healthy pubertal boys were enrolled as control. Growth parameters，sex hormone profiles，IGF-1，AMH and Inhibin B（INHB）were elevated at the beginning and after letrozole treatment.【Results】At baseline，no significant differences appeared in age，bone age， observation time，height for chronological age，height for bone age，midparental target height，BMI，or testis volume between two groups. After intervention，treatment group of bone age delayed，predict adult height increased，testicular volume increased and BMI increased compared with the control group（P=0.001，0.018，0.002，and 0.027，respectively）. The serum FSH，△FSH，LH，△LH，LH/FSH，T，and △T in the treatment groups were much higher（all P<0.001）， while the serum E2 and △E2 levels were obviously lower than the control group（P=0.043 and P=0.033，respectively）.17cases of control group and 13 cases of treatment group had serum AMH，INHB level tested before and after letrozole treatment. Serum AMH level in the control group appeared with a decreasing trend with the progress of puberty，while the treatment group showed the opposite tendency. And the △AMH was significant difference between control group and treatment group（P<0.001）. The serum INHB in the two groups increased in varying degrees after the intervention，the INHB level in control group increased more than the treatment group，but the difference was not statistically significant （P=0.517）.【Conclusion】Letrozole treatment can elevated levels of serum T with E2 reduce，bone age delay，predict adult height improved，and can obviously promote the secondary sex characters development in adolescent boys. And the longer letrozole treatment time，the more obvious growth effect. As to the reproductive function，letrozole may have inhibitory effect on testis maturity and cannot deny testis sertoli cells function affected with letrozole exposure.