The epoxidation of chloromethylbutenes by t-butyl hydroperoxide in the presence of Mo(CO)(6) has been investigated. The influence of important parameters on hydroperoxide conversion, selectivity of transformation to epoxy compound in relation to hydroperoxide used, yield in relation to olefin introduced (response function) has been described by regression equations in the form of a second order polynomial. The optimum values of : temperature, olefin to hydroperoxide molar ratio, reaction time, molar ratio of Mo(CO)(6) catalyst to hydroperoxide, ensuring the maximum values of these functions, have been determined.