The synthesis, fractionation and characterization of poly[bis(piperidino)phosphazene] are described. Dilute solution properties of the polymer in THF at 25 degreesC have been studied by size exclusion chromatography, using simultaneously multiangle light scattering and differential refractive index detectors. The anomalous elution behavior and the dependence of the dimensions, i.e, radius of gyration, of the polymer on the molecular weight are discussed. Coefficients for the scaling law have also been calculated.