The paper presents the results of the comparative research on the bactericid (lethal) effect of the exposure of a Escherichia coli bacterial culture to lethal UV radiation and the reduction of this effect by photoreactivation with visible light of the UV irradiated culture. As UV radiation source it has been used laboratory UV microbicidal (sterilisated) lamp (UV radiation,  = 254 nm). For the cultivation of control and irradiated bacterial culture of E. coli as well as for the numbering of the living cells/ml (TGN), there have been used the standard methods. The ultraviolet radiation has a differentiated bactericide effect on Escherichia coli cells, depending on the initial concentration of the bacterial cells and the irradiation time. The number of living cells in the E. coli bacterial culture that was exposed to the visible light action after UV irradiation (photoreactivation) is greater than that in the bacterial culture exposed only to UV radiation.