Abstract: In this paper a novel method is proposed for estimating number-average molecular weight from the intrinsic viscosity and GPC chromatogram of a sample for which the constants in Mark-Houwink equation is not known.The method was tested on seven sam-ples which have very different value of molecular weight and molecular weight distribu-tion.Results calculated by the method are in good agreement with those obtained using conventional method which requires constants of Mark-Houwik equation. The method is just approximate but fairly simple for number-average molecular weight determination.