The molecular displacements on the M-011-->M-101 phase transition of n-hexatriacontane (n-C36H74) have been investigated with an IR microscope designed for the oblique infrared transmission method. It has been clarified that two polytypic structures of the M-011 modification, single-layered structure (Mon) and double-layered one (Orth II), both transform to the M-101 modification of single-layered structure with their respective mechanisms. On the M-011(Mon)-->M-101 transition, the inclination direction of molecular axis is changed by 90degrees through an intermediate state in which the molecular chain is set perpendicular to the basal plane of the single crystal. On the other hand, a polymorphic-polytypic composite structural change on the M-011(Orth II)-->M-101 transition is accomplished through two kinds of molecular displacements occurring alternately along the stacking direction of molecular layers. (C) 2004 American Institute of Physics.