Nanotechnology evolution and the production of nano-medicine from various sources had proven to be of high value. Titania nanoparticles (NPs) are photoactive, potentially producing in vivo toxicity in the presence of light. The smaller the size of NPs is gaining importance in increasing research for the treatment of various diseases. In the present study, titania (TiO₂) and boron doped titania (B-TiO₂) NPs were synthesized using mangrove leaf aqueous extract and characterized using FTIR and XRD techniques. The toxic activity was evaluated on rotifers using different concentrations of suspended aqueous solution of pure and B-doped titania at various times (0.5, 1, 2, 4 and 24 h) at room temperature. The data show anatase structure with a diameter of 3 to 30 nm. The toxicity analysis revealed that the TiO₂ of different concentrations used doesn't have any toxicity in presence and absence of light source except a decrease in rotifer movement at high concentration, but B-TiO₂ show slow toxicity, which increases with increasing the concentration to attain a maximum value at high concentration at which 5% of rotifers died after 24 h and its immobilization reaches 23% in darkness. Overall, the best data are obtained in presence of visible light source.