The concept of Open Education (OE) is based on the philosophy of e-Learning which aims to provide learning environment anywhere, anytime, and for anyone. One of the main issue in the development of OE services is the availability of the quality assurance mechanism. This study proposes a metric for measuring the quality of OE service. Based on extensive literature review about e-Learning service quality guidelines, as well as the observation of existing Open Education services, we formulated Open Education Metric (OEM). OEM consists of 37 indicators which are divided into six criteria: (1) Openness, (2) Benefit, (3) Delivery, (4) Learning, (5) Evaluation, and (6) Support. Evaluation scheme is designed to give a clear guideline in assessing the quality of OE service quantitatively. The evaluation results including score and category indicate the overall quality relative to a set of indicators. Trial of evaluation was conducted using the evaluation system based on OEM to test its performance in evaluating OE service quality in institutions. Three of OE services were evaluated with their scores.