Knowledge of the ontogeny and development of vocalization in primates play a crucial role in understanding the evolution of the human language. Unlike the great apes, gibbons produce a remarkable vocal performance, which includes complex species- and sex-specific patterns. Many studies in the past focused on research of the acoustic pattern in adult individuals. Yet, it remains unclear how the males develop their sex-specific pattern of vocalization. This dissertation focuses on two specific periods in the ontogenetic development of acoustic structures in male Northern-white cheeked gibbons (Nomascus leucogenys) and Southern-yellow cheeked gibbons (Nomascus gabriellae). The results showed that the first time immature males (juvenile and adolescent) produced female acoustically structured great calls in duets with their mothers. How the great call was structured in immature males differed from the great call of their mothers; the difference being in spectro-temporal parameters from. The most significant difference between juvenile and adolescent males in the production of female vocalization was the presence of a twitter vocalization towards the end of their call. The results show that the twitter was a regular part of female vocalization in juvenile males around four years of age, while younger males produced this vocalization exceptionally. The second period in the ontogeny of vocalization in immature males (adolescent) was characterized by the fact that after five years of age, the development of the male acoustic structure begins. During this period, we did not observe the production of the female vocalization great call in any of the monitored Nomascus gibbon individuals. Results show that the ontogenetic process of the male song in Northern-white cheeked gibbons (N. leucogenys) did not develop in the same sequence as in adults which produced different notes and phrases. The immature male (adolescent male) first time developed the multi-modulation phrase (coda) and the staccato note (syllables) simultaneously at the beginning of this study, but, it was observed that they started producing the boom note four months later. Conversely, the development of the acoustic structure in male Southern-yellow cheeked gibbons (N. gabriellae) was characterized only by the development of a multi-modulation phrase. Development of the staccato syllables was not noted in this species during the study. The results support the interpretation that the development of the male acoustic structure closely corresponds to the growth of the vocal tract and physiological changes associated with reaching sexual maturity.