Diabetes mellitus is a metabolic disease characterised by hyperglycaemia due to impaired insulin secretion, insulin action, or both. The use of medicinal plants, such as forest bitter melon (Momordica balsamina) leaves, as an alternative treatment for diabetes is increasingly attracting attention. This study aimed to test the antihyperglycaemia effect of ethanol extract of forest bitter melon leaves and assess its acute toxicity. The research method was conducted by observing the blood KGD of mice induced by dexamethasone and sucrose. The mice were then treated with bitter melon leaf ethanol extract at concentrations of 10%; 15% and 20%. Acute toxicity test was conducted by Brine Shrimp Lethality Test (BSLT) method. Data were analysed with ANOVA test. The results of the antihyperglycaemia test showed a p-value = 0.035 (H0 rejected) which means there is a significant difference in the pre and post test KGD values with the most effective concentration reducing the KGD of mice is 20% with an average of 75 mg/dl. 50 Acute toxicity test showed LC value = 203.19 ppm (< 1000 ppm) indicating relatively high toxicity. In conclusion, ethanol extract of bitter melon leaves has antihyperglycaemia activity with a very toxic classification value.