To investigate conditions that affect the activities of diarrhea and antidiarrhea of rhubarb.Methods: Normal ICR mice,magnesium sulfate-induced diarrhoeal mice and diphenoxylate-induced constipated mice were used.Raw rhubarb with different dosages,processed methods and different decoction times were administrated to mice 2h after the diarrhoea and constipation models were induced.Results: 1）Diffenrent dosage: Raw rhubarb had antidiarrheal effect at the dose of 0.20 g/kg and significantly worsened diarrhea at the dose of 0.80 g/kg; rhubarb charcoal had antidiarrheal effect at the doses of 0.67-3.00 g/kg,and significantly worsened diarrhea at the dose of 5.00 g/kg.2）Different processing method: Raw rhubarb had laxative effect on normal mice with the dose of above 0.72 g/kg,on constipation mice at the dose of above 1.80 g/kg,and on diarrhea mice at the dose of 0.80 g/kg; while rhubarb charcoal 0.67-3.00 g/kg and cooked rhubarb 3.00 g/kg had antidiarrheal effect on diarrhea mice.3）Different decoctioning length: Raw rhubarb showed the strongest laxative effect at the decoction time of 10min,and the weakest laxative effect at 180min.Conclusion:The diarrheal and antidiarrheal effect of rhubarb act to conditions such as different physiological and pathological conditions,processing methods,dosages and decoction time.