Objective:To probe into the influences of different granule sizes and preparing procedures to rational clinical usage of rhubarb based on pharmacological equivalence.Method:The pharmacological equivalence of different preparing procedures

particle size（3-15 μm）

extract solvent（water and 70% alcohol）

extract time（15-20 min） and repeat times（1-6 times）

and pre-extracting or post-extracting

of rhubarb were compared regarding the defecation mass of constipated mice.Result:When extracted with water or ethanol

the maximum variations of laxative activities of rhubarb pieces in different sizes were of 4.5 or 2.0 times.Such variations of different preparing procedures

extract time

repeat times of extraction and pre-or post-extracting

were 1.7 or 1.7 times

1.3 or 2.4 times

1.9 or 1.4 times

respectively.The different preparing procedures investigated in the paper revealed significant influence to the laxative activities and those extracts were not pharmacological equivalent.When the rhubarb samples were extracted with water

the laxative activities in different repeat times of extraction revealed less difference while the post-extraction procedure revealed higher laxative activities than pre-extraction.Conclusion:The different preparing procedures for rhubarb showed significant influence to the laxative activities.The influence by clinical preparing procedures should be emphasized and the standard operation procedures（SOP） are need to be established.