Abstract: Water soluble photosensitive quaternary ammonium salts-containing acrylic phenolic resins(AQPR) were synthesized by reaction of epoxy phenolic resin with different tertiary amine hydrohalide salts to form different quaternary ammonium salt groups. Conversion, photosensitivity and thermal decomposition of the products were compared in order to find a suitable water developable, photosensitive solder mask. The results showed that with regard to reactivity TEA > TMA > DMA > TENA > TBA; HCl > HBr > HI. The resin obtained from TMA exhibited the highest photosensitivity, whereas those from TEA and TMA showed the best water solubility. During thermal treatment of the products containing both quaternary ammonium salt groups and epoxy groups at 160℃ for 0.5 h, besides partial decomposition, water insoluble component was formed, whereas the halide ions and epoxy groups of the thermal decomposition product diminished. This implies that at the thermal decomposition not only the halide ions diminished, but also crosslinkage were formed.