Low-temperature growth of ZnBeSe epilayer on GaAs substrates has been carried out at low-pressure (LP) by photo-assisted metalorganic chemical vapor deposition (MOCVD) using a ultrahigh-pressure mercury lamp as a light source. High-temperature growth of ZnBeSe has been also achieved by LP-MOCVD without light irradiation. It was found that the full-width at half-maximum of the diffraction peak of ZnBeSe epilayer increased with increasing irradiation intensity and growth temperature. The intensity of the emission band related to the excitons was obviously reduced due to poor quality of epilayer at high irradiation intensity and the deep-level emission band was predominant in the spectra.