While it is commonly known that sexual and love relations between men in pre-modern society, including that of the 'Abbāsid Period, were widespread, most of the historical research to date has regarded such relations as synonymous with modern concepts of "homosexuality." In addition, historians tend to be of the opinion that what may be called the "essentialist" concept of "Islamic homosexuality" has been embraced consistently regardless of time or place, when trying to understand male-male sexual relationships of various places and different periods. In recent years more and more research is being done that reexamines these conventional views. In particular, the research on the Ottoman Period has begun to relocate male-male sexual relationships within the context of sexuality as a whole. Unfortunately, the 'Abbāsid period has yet to be so reconsidered, mainly due to a paucity of historical sources regarding sexuality during that time. Given such circumstances, the present article is an attempt to show one facet of sexuality at the time, through a consideration of male-male sexual relationships in the 'Abbāsid period. For this purpose, the author conducts an analysis of the discourse presented in the al-Jāḥiẓ's Kitāb Mufākhara al-Jawārī wa al-Ghilmān (The Book of the Boasting Match between Girls and Boys) which is almost the only historical material written dealing explicitly with the subject of sexuality. The analysis shows that there was a distinction between "adult males" and "non adult-males," including not only females but boys, adolescents and so on, with respect to sexual relationships. Moreover, this distinction seems to correspond to a distinction between active and passive roles in sexual intercourse. The author concludes that sexual relationships at the time were based not on modern binary sexual categories of male and female, but rather on a different category fluctuating between "adult males" and "non adult-males."