This document describes a study that investigated the larvicidal potency of marigold stem and leaf extract against mosquito larvae. The study was conducted by three students from Madrid National High School in the Philippines as part of a regional science fair. They tested different concentrations of marigold extract in water containing mosquito larvae and observed the mortality rate over 38 hours. Statistical analysis using one-way ANOVA found a significant difference in the mortality rates based on the concentration of extract. The results suggest that marigold extract is an effective natural larvicide and could serve as a substitute for commercial larvicide in controlling mosquito populations.