Tensile drawing was carried out on nylon-6 films of different viscosity average molecular weights (M-v = 77 and 440 x 10(3)) and crystalline forms (alpha- and gamma-forms). The effects of M-v on the deformation behavior and the draw efficiency were discussed on the basis of the stress/strain curves recorded upon hot drawing, and wide-angle and small-angle X-ray diffraction, birefringence and tensile properties for the draw ratio (DR) series. The draw stress at a given strain and the fracture stress upon hot drawing were both higher for the higher M-v than for the low M-v, in either the alpha- or the gamma-form sample. For a given M-v, the draw stress was lower for the gamma-form than one with the alpha-form and the fracture stress was independent of the crystal forms, leading the former crystalline form to have a higher drawability than the latter, as previously reported. The M-v and the crystal form of predrawn samples had no effect on the crystalline chain orientation function (f(c)) measured as a function of DR. In contrast, the draw efficiency evaluated from the amorphous chain orientation function (f(a)) vs. DR and the tensile modulus and strength vs. DR was significantly higher for the higher M-v than for the low M-v. These drawing characteristics were discussed in terms of the entanglement effect and the deformability of the two crystal forms. The maximum achieved tensile modulus of 7.7 GPa and a strength of 760 MPa were thus obtained by the straight tensile drawing of the higher M-v sample that was initially a gamma-form.