Rotavirus represents the most common etiologic agent associated with diarrhea in the children both in developing and developed countries. Although the role of probiotic bacteria in the treatment of pediatric diarrhea is fairly well established, Probiotic dairy products are increasingly gaining popularity. We studied the effect of fermented yogurt containing lactobacillus on pediatric rotavirus diarrhea in north of IRIRAN tertiary referral hospital. This study was prospective randomized double blind controlled clinical trial in Booalisina children hospital for using probiotic yogurt in the treatment of acute rotavirus diarrhea between October 2009 - October 2010. Children between 6 months to 6 years presenting with acute watery diarrhea of less than 72 hours duration were screened for rotavirus infection by stool using Enzyme - Linked ImmunoSorbent Assay. All patients with acute diarrheal disease were randomized to receive probiotics (10(7)lactobacillus) fermented yogurt or non probiotic yogurt using in control group does not contain live bacteria. All patients received 100(cc) yogurts 3 times per day and ORS with a composition as recommended by WHO. We were interview or call parents every day until 72 hours. Data were analyzed by commercial software SPSS16. The difference between the 2 groups analyzed using t- test. The p value <= 0.05 was taken as statistically significant. 140 patients were randomized into 2 groups as case and control. A total of 20 cases were excluded for various reasons during the study and finally a total of 120 (60 in cases and 60 in control). Rotavirus identified in 48 patients (33.3% in control group, 46.7% in case group). Mean duration of diarrhea, duration of treatment and stay in hospital was compare in case and control group. No significance was observed in the frequency and duration of diarrhea between case and control group. In our study commercially fermented yogurt with 10(7) lactobacillus probiotics had no significant impact on minimizing any of symptoms in acute watery diarrhea or proven rotavirus diarrhea. We conclude, importantly, our study emphasized the need for a cautious approach towards commercially probiotic fermented yogurt in the acute management of diarrheal disease in children.