The study shows the effect of the disinfection process of real hospital wastewater on the behaviour of two reserve drugs, i.e. Linezolid and Aztreonam, and other physicochemical parameters of these wastewater, such as dissolved organic carbon, dissolved total nitrogen, etc. The studies were conducted in hospital wastewater, in which full-scale in-situ disinfection process was carried out, before it was introduced into the municipal sewage system. The samples were taken in winter and summer period. The results showed that the maximum concentration of Linezolid in hospital wastewater was equal to 2535.93 ± 95.44 ng/L and it was observed in the summer period. Each time the chlorine disinfection process caused the concentration of this drug in filtered wastewater after the process to be higher than before the disinfection process. This phenomenon requires further research, but a hypothesis was put forward that Linezolid in hospital wastewater occurs in a dissolved form and in conjunction with the wastewater suspension solids, and the disinfection process causes the disintegration of the suspension, which contributes to the increase in the concentration of dissolved Linezolid. It coincides with the increase in the concentration of dissolved organic carbon in the wastewater samples after the process.