In recent years, the emission of industrial wastewater has increased. Given the extremely wide industrial use of phenol, phenolic compounds are present in large quantities in wastewater. The presence of phenol in water can have toxic effects as a result of anthropogenic and natural activities. Phenols are most frequently bioaccumulated by natural processes and can disturb the bioecological balance. Even at low concentrations, phenols can have a negative impact on human health, while short-term exposure to high concentrations can lead to poisoning. Due to the high reactivity of phenol in the water medium, which is due to the presence of the hydroxyl group, phenolic compounds interact with inorganic components of the water environment and microorganisms. Ecotoxicological studies are carried out to assess the effects of phenol on aquatic organisms. In this work, the influence of phenol ecotoxicity on three microorganisms, the marine bacterium Vibrio fischeri, the microalgae Chlorella sp. and the bacterium Pseudomonas putida, was investigated. The tested concentrations of phenol were: 100 mg/L, 75 mg/L, 50 mg/L, 25 mg/L, 10 mg/L and 1 mg/L. During the experiment, bioluminiscence was measured for the bacterium Vibrio fisceri, and the number of live cells (CFU) of microalgae and the bacterium Pseudomonas putida during 3 days of exposure. The aim of the study was to determine the ecotoxicity of phenol on three organisms. The percentage of growth inhibition of the microalgae Chlorella sp. after 72 hours was 55.26%, while the growth inhibition of Pseudomonas putida was 46.97%. The maximum growth inhibition of Vibrio fischeri was 84.52% at the highest tested concentration of phenol (100 mg/L), so it can be concluded that Vibrio fischeri is the most sensitive of the tested microorganisms.