In this study, the safety dose of Eucalyptus camaldulensis hydrosol on carp (Cyprinus carpio) was investigated. Powdered eucalyptus leaves were mixed with deionized water and then distilled. The hydrosol was added into aquariums at doses of 0.05, 0.10 and 0.15 ml L-1 Temperature, pH, hardness and dissolved oxygen level of the water were recorded before and after hydrosol adding. The control and test experiments were repeated three times. Data obtained from the safety dose tests of E. camaldulensis hydrosol were evaluated using the Probit Analysis Statistical Method. The 5-h LC50 value (95 % confidence limit) of the safe dose of E. camaldulensis hydrosol was estimated to be 0.93 ml L-1(0.03-0.11). It can be seen that 0.05 ml L-1 doses of eucalyptus hydrosol do not create any kind of mental disorder. In the fish exposed to 0.10 and 0.15 ml L-1 doses, some mental disorders (rolling, numbness) and, at the end of 5 h, mortality in all the trial fish have been determined. The number of dead fish was significantly exposed to E. camaldulensis hydrosol (P<0.05).