Background: Vitamin D deficiency is highly prevalent among children worldwide. It causes impairment of the immune response to infection and decreased activity of gut antimicrobial peptides. The impact of vitamin D deficiency on the severity of acute diarrhea among children may be helpful for diarrheal management. Objective: To assess vitamin D deficiency and its correlation with recurrent acute diarrhea in children. Subjects and Methods: This study included 60 children, (1 to 5 years old) suffering from recurrent acute diarrhea more than 6 times per last year. They were subjected to complete history, clinical examination laboratory investigation and supplementation of vitamin D for three months for children who had vitamin D deficiency or insufficiency. Results: Vitamin D deficiency was found in 56.7%, insufficient in 21.7%, and sufficient in 21.7% in children with recurrent acute diarrhea. There was a statistical difference as regards the number of acute diarrhea attacks and vitamin D deficiency. Hemoglobin level was decreased below normal in (55%) of children with deficiency. Stool examination detected Enterobius vermicularis, Giardia lamblia, Entamoeba histolytica, and Ascaris lumbricoides in (26.7%, 8.3%and 3.3%, and 1.7%) respectively. Seventy-five percent of the studied children were supplemented with vitamin D which significantly decreases the number of diarrheal attacks. Conclusion: This study pay attention to the role of vitamin D in the susceptibility to infection-related illness in children. There is a positive correlation between vitamin D deficiency and iron-deficiency anemia. A significant decrease in the number of attacks of acute diarrhea after vitamin D supplementation was noted.