Water soluble photopolymers containing carboxyl as a water soluble group and benzalacetophenone as a sensitive group are easily synthesized by condensing of P (4-(vinylbenzyloxy) acetophenone-comethaclic acid) (P (4-(VBz) Ap-co-MA)) with benzaldehyde in the presence of alkaline catalyst between 0-2°C. Condensation polymer film was effectively crosslinked by the irradiation of UV light. They can be developed by commercial alkaline aqueous developing solution for nega type presensitized plate. The spectral sensitivity of these polymers were estimated 0.1 mJ/cm² (300 nm), 0.05 mJ/cm² (320 nm) and 0.06 mJ/cm² (340 nm), respectively.