In this report, polyamides were solution blended in the formic acid with poly(vinyl pyrrolidone)(PVP), an amorphous polar polyamide. The thermal behaviors and morphological change in the blends of Nylon 6 (PA6) and PVP were investigated in details via WAXD, DSC, FT-IR and POM methods. The equilibrium melting temperatures for PA6 in the blends were estimated based on the linear and nonlinear Hoffman-Weeks (LHW and NLHW) extrapolative methods. With increasing the mass ratio of PVP to PA6, T(m) (melting temperature) and T(c) (crystallization temperature) of PA6 in blends both decreased as well as that of the spherulite size of PA6. The interaction mode between PVP and PA6 was investigated by FT-IR spectroscopy, and the spectral changes indicated that the carbonyl groups of PVP had formed hydrogen bonding with the N-H groups of PA6 molecules in the molten state, which resulted in the variation of the morphology and thermal behaviors. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 375-381, 2012