Dexamethason is a hormone and corticosteroid-class drug produced by the adrenal gland and it function is to regulate carbohydrate metabolism, fat and protein, regulation of body fluids, the body’s defense system, and bone formation. The use of corticosteroid drugs must be considered properly because it can cause various side effects that are not good for the body. Dexamethasone is still widely used in the community without the right indication as an anti-inflammatory drug, rheumatoid arthritis, and anti allergic. This is due to a lack of knowledge about the side effects of corticosteroids. This study aimed to analyze the effect of education using leaflets on the level of knowledge and rationality of dexamethasone use by the one group pre-test/post-test study design with the Wilcoxon test. Respondents were taken with accidential sampling method. The number of respondents obtained was 47 respondents. Based on the results of this study can be concluded that education by leaflet administration can significantly increase knowledge and rationality of dexamethasone use in Sumber Sehat Pharmacy, Banjar.