Wool/polyester blended tops with different blend ratios are collected and made into fiber- bundle specimens for tensile testing. From the specific stress-extension curves of the blended bundles measured by the Sirolan-Tensor, the characteristics of the tensile curves are analyzed and the relationships between these characteristics and the blend ratios are discussed. Typical tensile curves, particularly the tail part of the curves, are used to evaluate the blend ratios of the fiber bundles. Three new approaches, the stress, work, and modulus methods, are developed for estimating fiber bundle blend ratios. The various parameters and algorithms of each method are defined in detail. The blend ratios calcu lated from the three methods are compared with the experimental values and with each other. There is a high coincidence between the experimental and theoretical results. The tensile behavior of WOOI/PET blended fiber bundles depends directly on their blend ratios.