Objective: To develop an assay methodology for determination of lumbrukinase potency in Rongshuan capsules., Method: The agarose-fibrin plate assay methodology for determination of Lumbrukinase potency in Rongshuan capsules was studied including durability, specificity, linearity range, product's handling method, accuracy , repetitiveness, solution stability, recovery and statistical method. The method of parallel line assay based on quantitative responses in statistical methods for biological assays was used in the statistics of potency assay., Result: The durability and specificity of assay accord with the requirement; The linearity range was 12.5 to approximately 400 U, the RSD of accuracy tests was 3.2%, the RSD of repetitiveness tests was 8.3%, the solution is stable under 4 degrees C for 72 hours, the recovery rate was 97.0% and the RSD of recovery assays was 16.5%., Conclusion: The agar-fibrin plate assay is rapidly, feasible, simple, convenient and accurate way for determining the Lumbrukinase potency. The method of parallel line assay based on quantitative responses in statistical methods for biological assays can control the error of determination.