Mangroves grow on the coast of large to small islands with unique ecology, known as a source of potential bioactive compounds. This study aims to evaluate the toxicity and potential bioactive compounds from leaf extracts of Rhizophora apiculata and Bruguiera sexangula growing on two small islands with different habitats, namely Payung Island and Maspari Island on the coast of South Sumatra. A total of 1,000 grams of leaf samples of R. apiculata and B. sexangula were taken from both islands and then dried in the sun using the indirect sunlight method covered with black cloth. A total of 100 grams of fine powdered leaf samples were macerated in 96% ethanol with a ratio of 1:10 (b/v) for 24 hours. Then the maceration solution was filtered and evaporated to a concentrated extract using a rotary evaporator at 60°C. Toxicity testing of extracts using the Brine Shrimp Lethality Assay (BSLT) method, and identification of toxic bioactive compounds in extracts, is done through phytochemical tests, total phenols, and GC-MS analysis. The test results showed that leaf extracts of R. apiculata and B. sexangula from Payung Island showed higher toxicity than those from Maspari Island, with LC50 values of 407 mg/mL and 337 mg/mL, respectively (medium toxic category), while those from Maspari Island were 654 mg/mL and 868 mg/mL (weak toxic category). Total phenolics in leaf extracts from Payung Island were recorded at 168.06 gGA/g for R. apiculata and 529.46 gGA/g for B. sexangula. Phytochemical tests identified the presence of alkaloids, saponins and terpenoids in both types of extracts from Payung Island, while GC-MS analysis revealed 20 bioactive compounds in R. apiculata extracts and 3 compounds in B. sexangula that have the potential as source of bioactive compounds for health and pharmacology