Abstract: This study attempted to shed some light on the effect of rubric-referenced peer assessment on EFL learners‟ speaking skill and on the cultivating the learners‟ awareness of having appropriate criteria for speaking, as one of the four major skills. This study explored the effect of rubrics on peer assessment of 18 Iranian EFL learners. First, learners assessed their classmates speaking performance based on their own presuppositions and assumptions. Subsequently, a spoken language rubric was introduced to them. They re-assessed their classmates‟ performances through using this rubric. Quantitative data analysis revealed significant difference between the results. In-depth qualitative analyses of comments and marginal notes written down by learners revealed that peers heed not only to institutional components specified in scoring scales but also to other irrelevant criteria such as the result of the speech act performed. The study has suggested that the use of a combination of peer assessment and rubric-referenced assessment encourages students to become more rationally responsible and reflective and has shown positive formative effects on student achievement and attitudes. The article concludes with some guidelines for practitioners. The findings of this study also provide insight into the effective assessment and recommendations for future research and practice are made.