To characterize the local conformations of ionenes, persistence lengths (P-1) were measured for 4,4-, and 6,6-ionenes (m,m-ionene) and 1,1-oxyethyleneionene (1,1-OEI) in methanol by small-angle X-ray scattering. It was found that P-1＇s of all the ionenes are almost identical (1.4 +/- 0.2 nm).