Polycaproamide (PCA) and cationic dyeable poly(ethylene terephthalate) (CDP) polymers were blended mechanically (in ratios of 75/25,50/50, and 25/75) in a melt twin-screw extruder to prepare three PCA/CDP poly-blended materials. The blends of PCA and CDP were spun into fibers.,The molar ratio of dimethyl 5-sulfoisophthalate sodium salt for CDP was 2%. This study investigated the physical properties of PCA/CDP polyblended fibers with nuclear magnetic resonance, gel permeation chromatography, gas chromatography, potentiometer, differential scanning calorimetry (DSC), thermogravimetric analysis, scanning electron microscopy (SEM), extension stress-strain measurements, density gradient analysis, and rheometry. The experimental results of DSC proved that PCA and CDP formed an immiscible system. In an SEM image of a 50/50 PCA/CDP blend, the morphological aggregation of a larger size, from 3 to 5 gm in diameter, was observed. The rheological behavior of the PCA/CDP polyblencled materials exhibited negative-deviation blends, and the 50/50 blend of the PCA/CDP polyblended fibers showed a minimum tenacity value. (C) 2003 Wiley Periodicals, Inc.