Five derivatives of diacetyl monooxime ester were synthesised by the reaction of diacetyl monooxime and corresponding acyl halides and used as photoinitiators. The relative photodecomposition efficiency by irradiation at 254nm UV light was decreased in the order of p-t-butylbenzoyl>p-methoxy benzoyl> benzoyl> dimethoxybenzoyl>acetyl derivatives and the photopolymerization tendency with MMA monomer was decreased in the order of benzoy1>dimethoxybenzoyl>p-t-butylbenzoy1>p-methoxy benzoyl>acetyl derivatives. The photopolymerization efficiency of these derivatives was superior or similar to that of the general photoinitiators such as benzoin, benzoyl peroxide and diacetyl. Molecular weight distribution of the polymers obtained by these photoinitiators was similar to that of the properties of typical radical photopolymerization.