Polystyrene films doped with anthracene or anthracene-d10 were ablated by 351-nm laser irradiation in a high-vacuum apparatus. Velocity distribution of ejected species were measured with a quadrupole mass spectrometer. Repetitively irradiated surfaces were found to differ from fresh surfaces in giving different velocity distributions. Hence, only the velocity distributions of the ejected species from the fresh surfaces were analyzed in detail. Below the ablation threshold, only intact anthracene molecules were detected, and their velocity distribution was analyzed by assuming a composite Maxwell-Boltzmann (MB) distribution with high-temperature MB (550-600 K) and low-temperature MB (250-300 K) components. When the etching of the surface took place at several hundred mJ/cm2, the detected species were mainly anthracene and styrene monomer. The translational energy distribution changed depending on the concentration of anthracene and the laser intensity. Deuteration of anthracene reduced the translational energy of both anthracene and styrene monomers. It was suggested that photon energy absorbed by anthracene is converted into thermal energy via rapid internal conversion in a polystyrene matrix, resulting in thermal decomposition of the matrix.