Recurrent infections and weak immunity were found to be linked with zinc deficiency especially in children. The goal of this study is to measure the level of blood zinc in children aged 6 months to less than 5 years old, and to assess the effect of 4 months of daily zinc supplements on the incidence and the severity of diarrheal morbidity. A randomized controlled trial study was conducted in Pediatric Outpatient Clinic in Ain Shams University Hospital on 140 children less than 5 years old who are apparently healthy. Random assignment of the sampled children to group receiving zinc (70 children) or group receiving placebo (70 children) was done. A questionnaire containing questions about occurrence of diarrhea was used during follow up. Serum zinc at baseline was measured. The mean age was 25.26 ± 15.7 months. Mean of serum zinc was 51.08 μg/dL, with 70% had low baseline serum zinc level. Cumulative incidence of diarrhea, number of diarrhea episodes per child and frequency of stools/day decreased significantly in zinc group ( P < .05). Risk ratio was found to be 0.79, 95% CI: 0.64 to 0.97. we concluded that incidence of diarrhea and its severity reduced in children received zinc daily for 4 months. This trial was registered at www.clinicaltrials.gov as NCT05002101.