Abstract: Disclosed is a linear acrylonitrile polymer having a viscosity average molecular weight of at least 50,000, which has a stereoregularity such that the polymer satisfies requirements of I>0.4 and (I+3S)>0.95, wherein I represents the fraction of the isotactic triad and S represents the fraction of the syndiotactic triad. A shaped article is made from a composition comprised of the linear acrylonitrile polymer and a solvent or plasticizer which is selected from a protonic acid and an aqueous solution thereof, an aqueous inorganic salt solution, and a mixture of an organic solvent and an inorganic salt. The fiber made therefrom has an enhanced drawability.