investigated the tensile strength and modulus of ultrahigh-strength polyethylene (UHSPE) fibers obtained by using the special two-step-drawing process of as-spun fiber (ASFs) which were prepared by the so-called gel-spinning method. We have found that the higher the ASF's spinning speed is, the higher the attainable tensile strength sigma(f) and modulus E are. For all the fibers drawn from ASFs with various spinning speed except for 120 m/min, we have found a master curve for the 1/2 inverse of sigma(f) which is plotted as a function of (TE-1/2)-E-1/4, where T is the linear density of the drawn fibers, in consistent with the Griffith theory: a thicker fiber obtained with a lower spinning speed exhibits lower strength, although all the AFSs possess the same value of E. This also suggests that a thicker fiber contains more defects which would lead to the Griffith-type crack propagation breakage. Moreover, from morphological observation of ASFs under transmission electron microscopy, the ASF obtained at a relatively low spinning speed possesses a heterogeneous cross-sectional morphology, whereas that obtained at relatively high spinning speed possesses a relatively homogenous morphology. We propose that this morphological evidence may account for the experimental findings of the behavior of the mechanical properties described above. (c) 2005 Wiley Periodicals, Inc.