【Objective】 To observe and evaluate the efficacy of clostridium butyricum with antibacterial for preventing diarrhea for children with pneumonia. 【Methods】 The children with pneumonia were randomly divided into three groups. The subjects from control group (n=100) were routinely treated with antibacterial. For those who suffered from diarrhea in the control group, clostridium butyricum was administered at doses of 0.5 g tid. In addition to antibacterial therapy, the subjects from observation groupⅠ(n=104) and the observation groupⅡ(n=101) administered clostridium butyricum at doses of 0.5 g, tid. After ending the antibacterial therapy, the children from observation groupⅠadministered the probiotics for more 7days at the same dose. The beneficial effects were observed. 【Results】 The incidences of diarrhea were reduced in the observation groupⅠand Ⅱ comparing to the control group (4.8% or 10.9%vs 32.0%; P<0.05). Both the duration of diarrhea and the period of treatment in the observation groupⅠand Ⅱ were statistically shorter (P<0.01) than those of the control group. Adverse reaction was not found. 【Conclusions】 Administration of clostridium butyricum powder may have some positive effects on children with pneumonia, who are treating with antibacterial for preventing diarrhea. It may be a better way to administer the probiotics for more 7 days after ending antibacterial therapy.