The study of triplet excited state behavior of DNA and its components is hampered by the very small yields produced by direct photolysis. Utilizing acetone sensitization method, a breakthrough for detection of triplet-triplet absorption spectra and triplet state kinetics of DNA components were performed at our laboratory,[1~5],. Very recently similar studies of triplet states of DNA components from acetone sensitization have been reported by Gut et al.,[6], However, comparative studies of triplet states of DNA components from acetone sensitization and direct excitation at similar condition have not yet reported. In this communication, the kinetic parameters of the decay of triplet states of thymine（Thy）, thymidine（Thd） and thymidine 5'-monophosphate （TMP） （Sigma Chemical Co.） have been obtained from both acetone sensitization and direct excition using 248 nm, 20ns excimer laser pulse in aqueous solution at room temperature. The self-quenching rate constant （k,sq,） and the rate constants of the unimolecular decay（k,0,） are listed in Table 1.