The active ingredient of pesticide roundup (glyphosate), N-(phosphonomethyl)glycine (NPMG), was exposed to UV radiation at λ = 250–600 nm. Ozone with the 2.5% oxygen content was bubbled through the NPMG reaction solution at a rate of 3.35 mmol h−1 (or 160.8 mg of ozone per hour). The decomposition NPMG is a complicated multistep process. It is practically impossible to identify NPMG in the solution after 14.3 h. The toxicological effect of both NPMG aqueous solutions and its phototransformation products were analyzed using the following assays: preparation of luminescent bacteria of the Ecolum series and infusoria Tetrahymena pyriformis. The cells of the latter were counted on a BioLat automated device with computer processing of the results. The toxicity of NPMG is retained until its 1000-fold dilution with pure water, while the 100-fold dilution of the irradiated sample was enough to eliminate its toxicity. It means that UV irradiation of NPMG together with its ozone treatment results in a 10-fold decrease in toxicity both in the case of Ecolum test system and that of T. pyriformis. The comparative study of the genetic effects for two genetic bacterial test systems shows that the phototransformation products contain substances with weak mutagenic and genotoxic activity. The obtained data indicate a high potential of the NPMG toxicity elimination method involving the UV irradiation of NPMG combined with the ozone treatment.