The twenty-first century African novel has been dominated by the younger generation of African female writers who are delving into tabooed areas like homosexuality, prostitution, incest, trafficking in women and minors, and issues that border on transnationality. Chika Unigwe’s On Black Sisters’ Street belongs to this generation. The novel captures the illicit business in human trafficking by the kingpin, Dele, in synergy with Madam, and the law enforcement agents in Antwerp, Belgium. The women who are trafficked into prostitution-Sisi, Ama, Efe and Joyce-are stripped of their identity and personhood. The thrust of the present research is, therefore, to examine the representation of these characters in the grammar of the clause. The aim of exploring the language of the text through the study of its characterization is to make for a fuller understanding of the text, as well as to investigate gender issues in the novel. Although the novel had been subjected to many analytical studies from diverse perspectives, yet, not much had been on the novel from functional linguistic perspective as the one employed in the present study. Thus, the present study is placed under Halliday’s Transitivity Theory in Systemic Functional Linguistics (SFL) to analyze the processes of transitivity that have been attributed to the male characters in contrast to the four female sex-slaves. The aim is to explore gender issues in the narrative. The data for analysis are the clauses, and the source of the clauses is the novel under investigation. A Purposive Sampling Method of data collection was used in extracting a corpus of data, which are analyzed qualitatively. The scope of the analysis covered only the four major transitivity processes, namely, the Material, the Mental, the Relational and the Verbal Processes, and the Participants involved in the Processes, because, these are the major Processes that can help to carry out the analysis of gender issues. The results of the analysis show that there is imbalance in agency between the male characters and their female counterparts. Dele, Titus, Brother Cyril, Janjaweed soldiers, etc are represented with Material Processes mainly as Actors in goal-directed Material Processes, and Verbal Processes as Sayers who can affect, influence, and take control of what is happening; while the female characters are represented as Goals in Material Processes who have things done to them; Mental Processes as Sensers.