One of the most irnportaiit morphological features of fibers is their cross-sectional shape. Nowadays, the circular fiber cross-section is the most common shape of melt-spun man-made fibers. Other shapes are begirming to ernerge for a variety of reasons such as performance, comfort, pilling propensity, bulkiness, tactility, processing etc. The filaments' cross-section can be easily varied by changing the spiruieret hole shape. Synthetic fibers that are predominantly spun by the melt spinning method with spimierets having the noncircular hole geometry are called profiled or noncircular fibers. Modifications of the fiber cross-section allow designing surface properties in yarn and fabric. However, the effect of profiled fibers on yarn properties has not been well documented yet. hi this article, the influence of different filament cross-section geometry on fiber properties was studied. PET (polyethylene terepfithalate) filament yarns having two different crosssectional shaped filaments, circular and cruciform, were manufactured by melt spinning. Differences in tensile properties of filament yarn and as well as of individual filament depending on the cross-sectional type were studied and revealed. More over, thermal and therniomechaiiical properties of filament yarn of both the cross-sectioos were studied and revealed by DSC and TMA method, respectively. (C) 2008 Wiley Periodicals, inc. J Appl Polym Sci 111: 805-812, 2009