A eco-friendly, cost effective, sustainable and green approach were used for the fabrication of silver nanoparticles by using leaf extract of Blumea lacera (Ag@BLE). Silver nanoparticles 9-13 nm sized were characterized by different analytical techniques. Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and Fourier-transformed infrared (FT-IR). UV-visible spectra were recorded, which showed a sharp surface plasmonic resonance (SPR) band at 429 nm and confirmed the formation of Ag@BLE. Organic dye methylene blue (MB) is one of the most abundant pollutants in the water environment. In the presence of catalyst Ag@BLE, the absorbance intensity of cationic MB dye was reduced dramatically by Sodium borohydride (NaBH4). The role and efficacy of AgNPs in the catalytic degradation of MB dye were studied, and the reduction rate were found to be 0.01455 min^-1 (0mg Ag@BLE, 21 min), 0.03144 min^-1 (20mg Ag@BLE, 24 min). Synthesized Ag@BLE showed rapid and excellent catalytic reduction of MB dye, and it follow pseudo first order kinetics.