The birefringent distribution of poly(ethylene terephthalate) (PET) fibers has been measured by means of Senarmont's compensation in this article. The difference from the traditional method is that two new approaches (i.e., measuring the shift of either straight fringes on a fiber cylinder or arched fringes on a fiber wedge) are established to figure out the cross-birefringence at different thicknesses of the fiber. Further, the fiber radial birefringent distribution is estimated by both using a series of theoretical models and their algorithms and by measuring with the fiber-wedge method combined with deferential calculation. There exists high coincidence between theoretical and measured values and the PET fiber is a skin-core structure of macromolecular orientation. Meanwhile, the experimental results show that (1) the double-angle measurement set a fiber at both the 0degrees and the 90degrees positions is necessary for high accuracy; (2) the setting of each optical element and the fiber is vitally important to obtain the exactly compensated values; and (3) the bulk birefringence is correlated with the measured initial modulus of the PET fibers. (C) 2003 Wiley Periodicals, Inc.