Diarrhea is the second leading cause of death in children aged 5 < years worldwide. Diarrhea is also a potential endemic disease of Extraordinary Events (Kejadian Luar Biasa/KLB) followed by mortality in Indonesia. Diarrhea is a disease that can be treated with self-medication. Knowledge affects attitudes and daily health behavior. When the knowledge is not sufficient, it may result in wrong drugs selection and finally therapy failure. Knowledge of diarrhea among mothers of toddlers indicates the ability to understand any information related to diarrhea, whereas parents with low levels of knowledge are twice more prone to a risk of suffering from diarrhea. Parents of toddlers must possess adequate knowledge to perform self-medication for diarrhea in children, therefore self-medication can be carried out accordingly and there are no medication errors. The purpose of this study was to determine the correlation between knowledge, attitudes, and behavior on self-medication of diarrhea among parents of toddlers in Parangjoro, Grogol, Sukoharjo, Central Java, Indonesia. This research is a cross-sectional study with a sampling technique using accidental sampling. The inclusion criteria in this study were mothers of children aged 5 years, agreed to be respondents, could read and write, had practiced self-medication, and followed research procedures. While the exclusion criteria for this study were parents whose educational or occupational backgrounds were in the health sector. The instrument used is a questionnaire. Data analysis applied the Spearman rank test. The results obtained that parents of children under five in Parangjoro, Grogol, Sukoharjo, Central Java, Indonesia had a moderate level of knowledge (73.3%), moderate attitudes (55.6%), and good behavior (73.3%). The level of knowledge implied a correlation to attitudes of 0.596 with a p-value of < 0.05 and the correlation between knowledge and behavior was 0.245 with a p-value of < 0.05. All things considered, there was a correlation between the level of knowledge, attitude, and behavior of self-medication for diarrhea among parents of toddlers in Parangjoro,