The oriented crystallization of linear low-density polyethylene (LLDPE) on high-density polyethylene (HDPE) has been investigated by transmission electron microscopy. From morphology and electron diffraction, it is confirmed that epitactic growth of LLDPE lamellae on the HDPE crystals takes place with an adoption of the HDPE crystal thickness at the interface and a continuous thinning of the LLDPE lamellae in the interface.