Aedes aegypti mosquito is a vector of Dengue Hemorrhagic Fever (DHF) that caused by the dengue virus. To prevent dengue disease one possible way is through the termination of the transmission cycle by means of vector control like using chemical insecticides. This research tried to explore the potential of natural product from seagrass as larvicide and to characterize the compound from different origin of samples to see their larvicide activities. One of the seagrass species, Thalassia hemprichii obtained from Prapat Agung Beach and Menjangan Island, West Bali National Park. Samples were separated by organ, i.e., leaf, rhizome and roots, and their origin. The samples dried powdered and then extracted using methanol with ratio 1:3 (w/v). After that, the extract characterized using High Performance Liquid Chromatography (HPLC). The extract bioactivity as larvicide tested, batches of 25 early third instar larvaes of Ae. aegypti tested to 1 % concentration of each from total four extracts and two control group of abate (0.01 %) and distilled water, all have the same volume. The observation was done in 12, 24, and 48 hours, then the percentage of individual mortality counted. The entire samples have 100 % mortality percentage, but the leaves of Thalassia hemprichii from Menjangan Island has the highest effectiveness where all larvae died within 12 hours. HPLC chromatogram showed the compound of T. hemprichii leaves, rhizome and root from two different places relatively had the same pattern. However, there is a different peak in Thalassia hemprichii leaves at Retention Time (RT) 5.880, that peak considers as the compound responsible for the effectiveness of larvacidal activity.