A simplified filter paper assay (FPA) method of cellulase enzymes was proposed based on high-performance liquid chromatography (HPLC) measurement. The method was according to the sum of glucose and cellobiose concentrations measured by HPLC that was able to be correlated with filter paper units (FPU) of the cellulase enzymes assayed by the traditional FPA method, regardless of the differences in the sources, activities, and components of the cellulases. This simple and quick assay method for the cellulase enzymes provided another parameter of the ratio of glucose to cellobiose (G/C ratio) representing the capacity of cellulase enzymes degrading cellulose into fermentable monomeric sugars.