Abstract: By analyzing the experimental principle, operating feature and limited factors of six classical test methods of ready biodegradability, it was pointed out that the suited test method, test substance concentration and inoculum concentration had better be selected according to the values of EC₅₀ and EC₂₀ of activated sludge from respiration inhibition test. After comparing the requirement on concentration ranges of test substances, source and pre-condition of inoculum, preparation and preliminary treatment of mineral medium, and validity of quality control of the six test methods, it was indicated that inoculum was forbidden to contact test substances before inoculating in all test methods of chemicals for ready biodegradability; different sources of inoculum might impact on test results greatly. Each method required different concentrations of inoculum, and it was suggested that bacteria should be enumerated by using plate-counting techniques and microbial cell densities controlled accordingly. The effective preliminary treatment of inoculum and mineral medium could reduce blank values. It was important to avoid organic carbon generated from filter membrane or centrifugation influence on analyzing DOC concentration. Frequent questions in test process were listed, and it was emphasized that test results should be estimated from degradation curve, and that trans-areas and multi-source standard inoculum should be researched and developed as soon as possible.