EPR detection of the photoexcited n-pi* triplet state of 3,4-dimethylacetophenone in durene single crystal is reported. The D and E values, principal directions of fine structure tensor, phosphorescence spectrum and the life time of the n-pi* tripiet state of 3,4-dimethylacetophenone are discussed. The comparison between these properties and those for pi-pi* triplet states of similar aromatic carbonyl compounds is discussed.