Abstract: The intrinsic viscosity, number average molecular weight and molecular weight distribution of a number of polydisperse cis-polybutadiene samples polymerized with lanthanide catalyst were determined by viscosimetry, osmometry and size exclusion chromatography.The procedures of the data treatment for the calibration of the SEC co-lumn,correction for axial dispersion and iterative calculation of the viscosity average molecular weights were given. The monodisperse Mark-Houwink equation of Ln-PB was obtained by linear regression between the experimental intrinsic viscosity and the calculated viscosity average molecular weight of the polydisperse samples.