OBJECTIVE： To observe therapeutic efficacy and safety of infantile infectious diarrhea treated with mezlocillin combined with Saccharomyces boulardii. METHODS： 96 patients with infantile infectious diarrhea were randomly divided into control group and observation group with 48 patients in each group. In control group， the patients were given mezlocillin， 75 mg/kg， tid. On this basis， the patients in observation group were given S. boulardii 250 mg， bid. Antidiarrheal time and healing time were compared between 2 group after 72 h， and bowel movement frequency ，clinical efficacy and security were observed before and after treatment. RESULTS： Antidiarrheal time and healing time of observation group were significantly shorter than those of control group， with statistical significance （P＜0.05）. 24 and 72 h after treatment， bowel movement frequency in 2 groups were reduced obviously； that of observation group was significantly less than control group 72 h after treatment， with statistical significance （P＜0.05）. The effective rate of observation group （95.8％） was significantly higher than that of control group （83.3％）， with statistical significance（P＜0.05）.  There was 1 case of constipation in observation group and 1 case of erythra in control group. Both groups were cured without special treatment. CONCLUSIONS： Mezlocillin combined with S. boulardii could cure infantile infectious diarrhea effectively and shorten the time of diarrhea and healing time， with good safety.