Nano-technology is a super microscopic technology to deal with the structures of 100 nm or smaller. This technology also involves the developing of TiO2 materials or TiO2 devices within that size. The aim of the present paper is to synthesize the silver doped nano-TiO2 by Sonochemistry method and to evaluate the effect of different percentages (0.2-1.5%) of silver load on TiO2 in the algae inactivation, The sample were characterized by using different techniques as XPS, TEM, SEM. Photo-catalytic activity of Silver doped TiO2 were evaluated through the inactivation of red tide (Cochlodinium) using UV-irradiation (315-400nm). The best result was found with silver doped TiO2.