This article considers whether the use of specific communication strategies can improve learners' English proficiency in communicative tasks. Japanese college students (n = 62) participated in a 12-week course of English lessons using a communicative approach with strategy training. To investigate the influence of specific strategy use, their performance on a posttraining conversation test was analyzed through multiple data collection procedures. Transcripts of the test were made and then analyzed in terms of production rate, the number of errors, and actual strategy use. An Oral Communication Strategy Inventory was introduced to elicit participants' communication strategy use for a self-report questionnaire procedure. These results were compared with participants' retrospective protocol data regarding their oral test performance. The findings confirmed that strategies for maintaining discourse and negotiation of meaning could enhance learners' communicative ability. Yet the students used a relatively small number of examples of modified output, which indicated that they might not have enough opportunities to improve the form of their utterances.