Citronella (Cymbopogon nardus L.) is a widely used plant in medicinal and agrochemical fields due to its unique secondary metabolite, citronellal. In this study, the chemical composition of citronella stem extract and its biopesticide activity against fall armyworm (Spodoptera frugiperda) was studied. Extraction of citronella with 96% ethanol was carried out using three methods, namely maceration, soxhletation, and microwave-assisted extraction (MAE). The chemical content in the extracts was analyzed using a GC-MS instrument. The potential of the extract as a biopesticide was carried out using the Completely Randomized Design (CRD) method by treating instar III larvae to citronella stem extract with a concentration of 0.5%; 1.0%; 1.5%; 2.5%; and 3.5% in triplicate. Data were analyzed using SPSS probit analysis. In silico computational study was done through molecular docking analysis. The results showed that the soxhletation method successfully obtained the highest citronellal percentage, 0.28%, compared to maceration (0.03%) and MAE (0.02%). Three citronellal compounds were detected in the extracts, namely citronellol, geranyl acetate, and hydroxy citronellol. The ethanol extract obtained by the soxhletation method was powerfully effective as a biopesticide with an LC50 of 0.456% in 12 hours of observation. Molecular docking analysis showed that all citronellal compounds contained in the extract had a binding energy lower than -5 kcal/mol indicating a potential bioactivity. Hydroxy citronellol had the lowest binding energy about -5.81 kcal/mol and two hydrogen bond interactions in Arg314 and Phe313 residues. It can be concluded that ethanolic extract of citronella stem can be used as a biopesticide, particularly against fall armyworm (Spodoptera frugiperda).