Display omitted •THM formation was generally higher during UV-chlorination.•HAN and HNM formation was generally higher during UV-chloramination.•Increasing UV dose enhanced the formation of DBPs during both processes.•Increasing bromide concentration shifted DBPs to more brominated species.•LP UV irradiation produced less DBPs compared to MP UV during both processes. This study investigated the effect of several factors on the formation of disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetonitriles (HANs) and halonitromethanes (HNMs) during UV-chlor(am)ination of the water collected after filtration unit in a drinking water treatment plant. In general, THM formation was higher during UV-chlorination while HAN and HNM formation were higher during UV-chloramination. Higher Medium pressure (MP) UV dose resulted in more DBP formation. The value of pH affected DBP formation differently. THMs decreased with increasing pH during UV-chlorination but remained stable during UV-chloramination. HNMs increased as pH increased from 5 to 7 but decreased as pH further increased to 9 during UV-chlorination. On the other hand, HNM formation decreased with increasing pH during UV-chloramination. However, pH had little impact on HAN formation. The nitrate concentration had negligible impact on the formation of THM, HAN and HNM during both UV-chlor(am)ination. Increasing bromide concentration improved THM and HAN formation, decreased HNM formation, and shifted DBPs to more brominated species in the three categories. MP UV irradiation enhanced the formation of DBPs compared to low pressure UV during both UV-chlor(am)ination, especially for nitrogenated DBPs.