Background: Street children are children aged 5 to 18 years who are working actively in the street in urban areas. Due to their whole-day-life on the street, street children are being susceptible to diseases one of them is diarrhea. On the other hand, their opportunity to get information about diarrhea is not quite enough because they spent their time to work on street. Aim: The aim of this study is to enrich the knowledge of street children about diarrhea through health education in the form of counseling, discussions, and simulations. Methods This study was quasi experimental with pre and post test group design. Respondents in this study were street children aged 8 to 13 years working actively on the streets as many as 20 children. The first step were done an interview to get pre test data. Then, respondents were given health education. In the end of this study, they were interviewed to get post test data after 2 weeks later. The data was described in table form and graph and analyzed with Saphirowilk test for the normality of the data. As the spread of data was not normal, it continued by transforming the data. After transforming the data, the data still was not normal. Furthermore, the writer analyzed with wilcoxon test to know the effect of health education for street children’s knowledge about diarrhea . This data analysis usedSPSS Result: Wilcoxon test p= 0.000 showed that there was a significant difference of street children’s knowledge about diarrhea before and after they got health education. Conclusion: Health education in the form of counseling, discussions, and simulations could enrich the knowledge of street children about diarrhea with significant development in Semarang. keyword : health education, street children, knowledge, diarrhea.