Diarrhea is a cause of high mortality in children. Zink is an elemental substance that is widely used for the treatment of diarrhea in children. This study aimed to determine the effectiveness and side effects of zinc usage on diarrhea in children outpatient at Apotek Indah Farma from April - July 2018. This type of research is cohort with observational analytic research design. Data collection was carried out prospectively by observing prescription for diarrhea for outpatient children. Sampling determination by consecutive sampling with inclusion and exclusion criteria as consideration. Analysis of the results of therapy was done by calculating the duration of healing / duration of diarrhea. Respondents in this study were 20 outpatient children with diarrhea and divided into zinc and non-zinc therapy groups. To find out the length of recovery of diarrhea, an interview with parents was conducted. Analysis of data was used independent sample t test and Mann Whitney test as non parametric alternatively. The results of this study showed that children with diarrhea that had a zinc therapy had a significant decrease in the duration of diarrhea P = 0.00 (<0.05) and a decrease in diarrhea frequency P = 0.00 (<0.05). Side effects of zinc in diarrhea patients were not found.