In this article, canonical correlation analysis was used to explore the relationship between the  toxicity-attenuating effect and the variation of chemical contents in rhubarb caused by processing.  With quasi-acute toxicity test, the difference of hepatic and renal toxicity to mice with the processed materials of  rhubarb was researched.  The chemical contents of anthraquinones and tannins in rhubarb were measured by UV-vis spectrophotometry and high performance liquid chromatography.  The results showed that there were toxic effects to liver and kidney in mice after repeated intragastric administration of rhubarb and its processed materials for 14 days at a dosage of 76 g·kg⁻¹.  The toxic effect of processed materials was much lower than crude drug.  With canonical correlation analysis, the sequence of the hepatic and renal toxicity of chemical  contents in rhubarb were found as follows: total anthraquinone glycosides (AQGs) > tannins (Tns) > total      anthraquinones (AQs); aloe-emodin (AE) > physcione (Ph) > rhein (Rn) > emodin (Ed) > chrysophanol (Ch) and AEG > PhG > ChG > EdG > RnG of glycosyl-anthraquinone.  It could be concluded that processing would   attenuate the toxicity of crude drug of rhubarb.  The toxicity-attenuating effect might be correlated to the    decline of the contents of both anthraquinone glycosides and tannins, especially the aloe-emodin glycoside and physcione glycoside.  The results also suggested that the serum alanine aminotransferase (ALT) and creatine (CREA) would be useful to monitor the hepatic and renal toxicity of rhubarb.