Objective To explore a quantitative method of causality assessment of adverse drug reactions (ADR). Methods By means of literature review and expert consulatation, 14 indexes of criteria level in ADR causality assessment were obtained, sub-criteria level was established for each parameter accordingly, and a questionnaire was designed. Sixty-five professionals in ADR assessment from Shanghai Food and Drug Administration and medical institutions of all levels in Shanghai were surveyed and asked to complete the questionnaires based on their knowledge and experience. Analytic hierarchy process and synthetic index method were employed to establish the quantization standard of ADR causality assessment. Ten cases of ADR reporting to national ADR monitoring center from a given company were randomly selected for demonstration. Results Index weights at criterion level and sub-criterion level were drawn after calculation, and a five-grade quantitative criterion of ADR causality assessment was proposed. The results of demonstration with 10 cases were consistent with the available findings. Conclusion The proposed fivegrade quantitative method of ADR causality assessment can serve as referrences for ADR compensation mechanism.