The Serra dos Tomazes, located in the Pirai District, RJ, consists of an intrusive alkaline body, composed mainly of micronepheline-syenites. This alkaline body intrudes metatexites of the "Paraiba do Sul" folded belt. Mylonitic Zones we re recognized south of the intrusive alkaline body, and they may be associated with the Alem Paraiba Lineament. This lineament corresponds to an ENE striking transcurrent fault. This fault belongs to a system of transcurrent faults that is called the "São Paulo Transcurrence Zone". The strike-slip faults that form the bulk of the "Sao Paulo Transcurrence Zone" are generally right-lateral. The Serra dos Tomazes alkaline body is probably associeted, in time and in origin, with other alkaline intrusions in the State of Rio de Janeiro. This alkaline magmatism seems to be associated, at least geographically, with the "Sao Paulo Transcurrence Zone".