A basic study on crystal structure and orientation behavior of transversely compressed ethylene-1-octene copolymer with different 1-octene contents was described. All polymers were first melt spun under different spinline stress and subsequently transversely compressed. For the melt-spun filaments, an orthorhombic crystal structure was found for all polymers, but a pseudo-hexagonal mesophase was also found for polymers with the highest 1-octene level (13.3 mol%). For the transversely compressed filaments, several reflection peaks from a monoclinic unit cell were found for polyethylene without octene. For those with higher octene levels, the reflection peaks from monoclinic became fainter and disappeared for the one with the highest 1-octene level. After being transversely compressed, the (110) and (200) peaks of orthorhombic crystal structures became oriented along the meridian direction, which is the fiber axis direction. The reason for this appears to be that the compression deformation of the filament induces elongation along its width direction and shrinkage along its length and thickness direction, and in this change the polymer chain orients. POLYM. ENG. SCI., 48:2297-2304, 2008. (C) 2008 Society of Plastics Engineers