Narrowed spectra at 452 nm from a thin platelike crystal of distyrylbenzene derivative, 2,5-diphenyl-1,4-distyrylbenzene with two trans double bonds (trans-DPDSB) grown by vapor deposition, are observed. The trans-DPDSB crystal is irradiated by the third harmonic (355 nm) of a Nd:YAG laser. The FWHM of the narrowed spectra can reach 6 nm for the crystal when the pumping energy is 400 microJ/pulse. The threshold value for an optically pumped laser is approximately 350 microJ/pulse.