The present study evaluates the efficacy of crude extract and synthesised silver nanoparticles (AgNPs) of leaves and stem of Ranunculus sceleratus L. against immature larval stages of Culex quinquefasciatus. Different concentrations of crude extract of both plant parts were tested against 1st to 4th instar larval stages, and synthesized AgNPs were tested against 3rdinstar larvae of Cx. quinquefasciatus. The characterisation of synthesized silver nanoparticles (AgNPs) was also carried out. The antioxidant activity of the methanolic extract of both plant parts was also explored. A 100% mortality was observed in 1% crude extract and 5 ppm of synthesized AgNPs of leaves and stem of R. sceleratus against 1st and 2nd instar larvae, respectively. The UV–Vis spectrophotometer confirmed the synthesis of AgNPs where the absorption maximum (A0) was recorded at 450 nm and 440 nm, respectively, in leaves and fruits of R. sceleratus. The scanning electron micrographic (SEM) of the AgNPs indicates that almost all the particle’s surface is rough in shape. The core shell morphology of synthesised AgNPs were identified by FTIR measurements. 80 μL concentration of methanol extract of both the plant parts almost completely inhibited DPPH with IC50 values of 44.93 and 22.17 μL, respectively, in the leaves and stem of R. sceleratus. It is concluded that both the plant parts of R. sceleratus showed excellent mosquito larvicidal activities and good free radical scavenging activity