Armyworm (Spodoptera litura) is a type of pest that attacks tomato plants. Yield losses due to this pest attack can reach 80%. Most farmers control this pest using synthetic pesticides. Although effective, the use of synthetic pesticides has adverse side effects on the environment and health. To reduce these side effects, one alternative is to use natural pesticides that are more environmentally friendly. Several studies have been carried out, including the extract of Tigaron leaf with an extract concentration of 16% causing a mortality of 23.33%, while Bintaro leaf extract with a concentration of 100 g/l caused a mortality of 40%. Both of these results are still classified as ineffective. Therefore, it is necessary to alternatively use other plants as natural pesticide ingredients. This study aims to determine the effectiveness of mahogany seed extract on the mortality of armyworms that attack tomato plants. This study used an experimental design in the form of a completely randomized design (CRD). The treatments tested were mahogany seed extract with concentrations of 5%, 10%, and 20%. As a comparison, the synthetic pesticide DuPont Lannate 25 WP was used with a dose of 1 gr/l (positive control), and no treatment (negative control). Each treatment was repeated 3 times. Parameters observed were armyworm mortality for 24 hours and observed every 4 hours. Data were analyzed using analysis of variance (ANOVA) with F test. The results showed that mahogany seed extract had a significant effect on armyworm mortality. The highest mortality was found in the P3 treatment (20% mahogany seed extract) which was 50%. This result is higher than previous studies, but still cannot be said to be effective.