Background: The insecticides of microbial origin may serve as suitable alternative biocontrol agents. The present study aimed to identify the major chemical constituents and test the larvicidal toxicity of Serratia marcescens against Aedes aegypti and Culex quinquefasciatus mosquitoes. Materials and Methods: The mosquito bioassay test of four different concentrations (100, 200, 300 and 400 ppm/ml) of bacterial extracts was performed as per standard protocols. The chemical compounds and its functional groups were identified by GC-MS and FT-IR analysis, respectively. Results: The larval bioassay results observed better effect with the varied levels of LC50 and LC90 values. Six major compounds identified by Gas Chromatography Mass Spectrophotometer (GC-MS) and named as follows: 1-o-monoacetyl-2, 3-o-dibenzoyld- ribofuranose (20.255%), 1-butanol, 3-methyl-, benzoate (19.380%), Bentiamine (18.855%), Benzoic acid 2-bromoethyl ester (18.415%), and Cyclotrisiloxane hexamethyl- (2.658%). Fourier transform infrared spectroscopy (FT-IR) spectral analysis reflect the functional groups of (aromatic, alkynes and amines) the biomolecules. Conclusion: We found the increased level of larval mortality based on extract concentrations and exposure time.