A novel polar material, KSr4B3O9, has been obtained by the high temperature solution method for the first time. It crystallizes in the polar space group Ama2. The material exhibits a three-dimensional structure consisting of interconnecting KO10 groups, SrOx (x=8, 9) units and isolated BO3 triangles. DSC/TG curve shows that KSr4B3O9 melts incongruently. The calculated band structures and the density of states of KSr4B3O9 suggest that its direct gap is 3.897 eV. The absorption spectrum indicates the absorption edge of KSr 4B3O9 is about 302 nm. It produces SHG intensity about as large as that of KH2PO4 (KDP) and is phase matchable.