Sesbania grandiflora Linn. (Family: Fabaceae) is widespread distributed in West Bengal, Assam, Karnataka and North-Eastern parts. The present study intended with various phytochemical screening and toxicity studies on Sesbania grandiflora. The present study was done with the help of soxhlet extraction, Kirby Bauer well diffusion assay, Minimum Inhibitory concentration assay (MIC) and Colony forming unit (CFU). Preliminary phytochemical evaluation of the aqueous extracts revealed that presence of carbohydrate, proteins, flavonoids, alkaloids, tannins and glycosides. As per the antimicrobial investigations in the presence study the CLP (Crude Leaf Powder) of Sesbania grandiflora exhibited low level antibacterial activity but the NPL (Nanosized leaf powder) exhibited highest level of antibacterial activity.