Beta-cypermethrin, a synthetic pyrethroid pesticide and potential toxic pollutant, was investigated in the present study for acute toxicity to Nile tilapia (Oreochromis niloticus L.) fingerlings. The bioassay experiments were repeated three times and the 24-hour LC50 was determined for the Nile tilapia. A static test method of acute toxicity test was used. Water temperature was regulated at 21±1°C. In addition, behavioural changes at each beta-cypermethrin concentration were observed for the individual fish. Data obtained from the beta-cypermethrin acute toxicity tests were evaluated using the probit analysis statistical method. The 24-hour LC50 value for Nile tilapia fingerlings was estimated as 21.4 μg/l (12.5-30.2).