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The present study was aimed to test the efficacy of Leptogium marginellum (Lm) extract and synthesized silver nanoparticles (AgNP's) against mosquito larvae. The synthesized LmAgNP's was measured for its Surface Plasmon Resonance and the peak was observed at 428nm. FTIR results recorded a downward shift of absorbance band between 450-4000 cm-1 indicated the formation of Lm AgNP's which are spherically shaped with a size range from 150-200 nm confirmed using FESEM. Further, XRD analysis demonstrated LmAgNP's are highly crystalline and exhibit a cubic, face centered lattice with characteristic (111), (200), (220) and (222) orientation. The bio-reduction of silver ions in solution was monitored by EDX. The zeta potential value was found to be -3.08 mV representing AgNP's were highly stable. Radical scavenging results revealed that the extracts and AgNP's demonstrated potent scavenging ability evidenced by DPPH, FRAP and H2O2 radical assay. Lm fractions and Lm AgNP's exhibited dose dependent larval mortality, highest mortality was observed in ethylacetate fraction against Anopheles stephensi (ICc50=34.66; IC90=158.647), followed by Culex quinquefasciatus (ICc50=40.085; IC90=213.777) and Aedes aegypti (IC50=70.673; IC90=248.836). Larvae treated with LmAgNP's at different concentration represented potent mortality but at 500 ppm concentration demonstrated significant mortality with 88, 94.4, 98.4% mortality with highest activity against Anopheles stephensi (ICc50=47.41) followed by Aedes aegypti and Culex quinquefasciatus (IC50=71.66; IC50=74.44). Based on the present findings it is suggested that the fractions and AgNP's of Lm is effective in inhibiting the growth of mosquito larvae. [ABSTRACT FROM AUTHOR]