Legionella pneumophila is an ubiquitous molecule to which the water supply network, swimming pools, heating, air conditioning and ventilation systems represent favorable conditions for growth and development and are key sources of infection. It is spread by aerosol and, causing Legionnaires' disease and Pontiac fever, represents a significant public health problem. Its biofilm formation and the ability to reproduce within protozoa provide protection and resistance to disinfectants. The purpose of the conducted research is to show the impact of ozone on L. pneumophila. Three different types of biofilm cultivation materials were used including polystyrene, stainless steel and ceramic tiles. Additionally, the effect of ozone on the formation of biofilm on polystyrene was observed in the presence of broth enriched with L-cysteine and iron (III) nitrate. Finally, the impact of ozone was tested on free bacteria L. pneumophila in water. Biofilm cultivation for each individual material was carried out over 24 hours and 5 days. The method of treatment for both time periods is the same. The materials were washed with an appropriate solution and left to dry for 5 minutes. Then they are exposed to ozone, which was blown by the ozonizer for 38 seconds for an hour. They were then treated in an ultrasonic bath for 1 minute and then a series of tenfold dilutions was made. After inoculation on BCYE agar and cultivation at (35±1)℃ for 4 days, CFU/mL was determined by colony counting. Only free planktonic bacteria were treated with ozone immediately before preparation of the suspension without prior 24-hour or five-day biofilm cultivation. For each treated material and free planktonic bacteria, a control sample subjected to the same treatment, with the exception of ozonation, was comparatively prepared. The inhibitory effect of ozone has been proven on polystyrene, stainless steel and ceramic tiles. After the treatment and incubation of the agar, no growth of bacteria was observed, and we conclude that the effect of ozone was 100% effective. Ozone did not have the expected effect on the free planktonic bacteria L. pneumophile and its effect was negligible. Ozone also did not prevent biofilm formation in broth enriched with L-cysteine and iron (III) nitrate.