Alkyl hydropercuddes are found to be important intermediates in the combustion and oxidation processes of hydrocarbons. However, studies. of ethyl hydroperoxide (CH3CH2OOH) are limited. In this work, kinetics and mechanisms for unimolecular decomposition of CH3CH2OOH have been investigated. The potential energy surface of decomposition reactions have first been predicted at the CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311G(d, p) level. The results show that the formation of CH3CH2O + OH via O-O direct bond dissociation is dominant, the branching ratio of which is over 99% in the whole temperature range from 300 to 1000 K, and its rate constant can be expressed as k1 = 9.26 x 10(52)T(-11.91)exp(-26879/T) s(-1) at 1 atm. The rate constants of the reaction CH3CH2OOH -> CH3CH2O + OH at different temperatures and pressures have been calculated, which can help us to comprehend the reactions of CH3CH2OOH at experimental conditions.