The study focused on investigating the impact reciprocal peer tutoring teaching approach has in promoting interest among senior secondary school students in writing expository essay in Igbo –Etiti Local Government Area, South-East, Nigeria. The effect of gender in promoting interest in expository essay writing among senior secondary school students was also investigated. Two research questions and three null hypotheses guided the study. The study adopted a quasi- experimental design. 75 (32 males and 43 females) in two intact classes consisted of the sample for the study. Expository Essay Writing Interest Inventory (EEWII) which was face validated by four consultants was used as an instrument to data for the study. Mean, standard deviation and analysis of covariance (ANCOVA) were used to analyze the data collected. Results obtained revealed that reciprocal peer tutoring teaching approach was effective in promoting interest in expository essay among the students. The result also indicated that the variation in the mean interest scores of male and female students in expository essay was not significant. The interaction effect of gender and the teaching approach on mean interest scores of senior secondary school students in expository essay writing was also not significant. Hence, the researchers recommended that secondary school teachers should adopt this teaching approach for expository essay writing teaching in secondary schools.