We investigated the in-situ molecular orientation behavior of isotactic polypropylene (iPP) films under simultaneous and sequential biaxial deformation by polarized infrared spectroscopy at near melting temperature. The three-dimensional orientation functions in two stretching directions (in-plane of the film specimen) and its thickness directions were obtained from the dichroic ratios of two bands with different transition moments. Equi-biaxial stretching was found to cause iPP chains in both crystalline and amorphous regions to rotate towards the stretching plane. However, under sequential biaxial elongation, the iPP chains in both regions first oriented towards the first stretching direction and then rotated to the second stretching direction during the second stretching process. (C) 2015 Elsevier Ltd. All rights reserved.