The effect of strain rate and gauge length on the Weihull distribution fitness of Kevlar fibers and the influence of twist density on the fracture behavior of high tenacity fibers such as Kevlar, glass and carbon liber were studied to characterize the specialty fibers. For fitting the Weibull distribution, two experimental conditions were used. One was that strain rate was changed to 0.01. 0.04. 0.1, 0.4, 1.0 min-1 with constant gauge length(50mm) and the other was that the strain rate was kept constant at 0.1 min-1 with different gauge lengths(i.e., 10. 50. 100. 200mm). The results obtained in this study are as follows 1) The strength of Kevlar fibers increased with increasing strain rate and the trend was well fitted to Weibull distribution with various strain rates. 2) The strength of Kevlar liberal dccrcased with increasing gauge length. Especially, when gauge length Increased from 10mm to 50mm. the strength value decreased conspicuously about 12.1% and Weibull distribution was well fitted for strength values with various gauge lengths. 3) The fracture mechanism of high tenacity fibers with twist density showed that the dislocation and/or flaw took place on the fiber surface and the crack developed along fiber axis. Also, the failure shape of Kevlar fiber had long fibrils, but glass antral carbon fiber had the brittle fracture in fixed direction.