Ketapang is a plant that has been used traditionally to treat various diseases, one of which is diabetes. Ketapang is also known to contain medicinal compounds flavonoids, triterpenoids, tannins, alkaloids, steroids and fatty acids. The aims of the study were to determine the effect of dried ketapang leaf extract on alloxan-induced blood sugar levels in mice and to determine the effective dose of dried ketapang leaf extract in reducing blood sugar levels in mice. This study is an experimental the stages of this research include plant identification, manufacture of dry simplicia characteristics, phytochemical screening of sintrong leaves, sintrong leaf extraction, as well as testing for antidiabetic activity study using 25 rats and divided into 5 groups that is CMC Na 0,5% as a blanco and group 1 (negative control), groups 2 (positive control) glibenclamide, group 3, 4, 5, dose of 200 mg/kgbw, 300 mg/kgbw, and 400 mg/kgbw. Giving to rats orally and measuring blood sugar levels. Blood sugar levels were set at the beginning of fasting, days 6, 8, 12,16. Blood sugar levels in each group were analyzed statistically using the one way ANOVA method. The results of the phytochemical screening of ketapang leaf contain alkaloids, flavonoids, tannins, saponins, glycosides, steroids and triterpenoids. The results obtained were that the three doses of ketapang leaf extract could significantly reduce the blood glucose levels of mice compared to the positive control group. The decrease in blood sugar levels resulting from the administration of ketapang leaf extract was greater. So that the administration of ketapang leaf extract has an antidiabetic activity effect in diabetic mice at doses of 200mg/kg BW, 300 mg/BW, 400mg/kg BW.