The present study examined whether oral interactive (pair) rehearsals and individual rehearsals promote second language (L2) learners' communication ability. The participants were 60 first-year students from two required English classes at a national university in Japan. One class was designated as 'the compulsory rehearsal' group (CR, n=28); the other as 'the free rehearsal' group (FR, n=32). In class, participants engaged in a five-minute conversation in pairs five times on different topics during the course, while at home, they were required (CR) or encouraged (FR) to engage in two interactive rehearsals with a partner and five individual rehearsals per conversation. Pre- and post-conversation tests were conducted in pairs, and each student's performance was assessed using a rubric developed for this study. Multiple regression analysis showed that the frequencies of both an interactive rehearsal and an individual rehearsal were significant predictors of the students' improvement in the conversation test (R[superscript 2] = 0.304, Interactive Rehearsal: [beta] = 0.37, p < 0.05, Individual Rehearsal: [beta] = 0.39, p < 0.05). It also revealed that interactive rehearsals helped learners improve their L2 communicative ability, while individual rehearsals were likely to improve their ability to express their ideas.