The developing discourse which moves assessment away from a measurement model towards one of learner empowerment and the development of assessment for lifelong learning sets the context for this article. The aim was to investigate the effect of self-assessment on foreign language learners' oral performance ability. Twenty EFL students of foreign language institutes in Tokyo participated in the study. They were divided into an experimental group and a control group, based on the results of English oral performance pre-tests. The research instrument consisted of a self- assessment checklist containing subcategories related to the organization of the presentation, content, linguistic factors (vocabulary use, grammatical rules and pronunciation) and interaction with the audience. It was developed as a result of interviewing participants and their teachers and then adapting results based on the results of reviewing available checklists in the literature. The data were collected by the experimental group members' self-assessments of their 6 oral performances and the teacher's assessment of their performances. The obtained data was analyzed using descriptive and inferential methods. Results indicated that participating in self-assessment process had positive effect on learners' oral performance ability.