Green synthesis of nanoparticles is becoming one of the robust techniques, which may be suitable alternatives for chemical and physical methods. This study reports a cost effective and environmental friendly green synthesis of titanium dioxide nanoparticles (TiO2 NPs) using Sesbania grandiflora. The biosynthesized TiO2 NPs were characterized by Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and Transmission Electron Microscopy (TEM), Ultraviolet-visible spectrophotometry (UV-Vis) and X-ray powder diffraction (XRD). FTIR spectrum confirmed the involvement of alkynes, alkanes, flavonoids and secondary alcohols in the capping and reduction of TiO2 NPs while XRD characterized the crystallographic plane of the rutile phase of TiO2. Size of TiO2 NPs was in the range of 43-56 nm and EDX showed a strong TiO2 signal. The phytosynthesised TiO2 NPs were used for zebrafish embryo toxicity tests, which were performed to monitor the changes in the toxicological effects. Besides, the model adapted in this study was suitable to explore the toxicity in Zebrafish. TiO2 NPs increased bioavailability and uptake into cells and organisms. In order to assess the TiO2 NPs toxic level we employed the fish model as aquatic environment. This study demonstrates that TiO2 NPs are lethal to zebrafish.