The structural and physical properties of polyamide 66 (PA66)/syndiotactic polystyrene (sPS) blends were studied with electron microscopy, wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis, and tensile creep, stress-strain, and impact measurements. Attention was primarily concentrated on blends with sPS weight fractions (w(2)) in the range of 0 < w(2) <= 0.50. DSC and WAXS showed that the integral crystallinity of the PA66 and sPS components in the blends was virtually unaffected by the blend composition. Polymorphism of sPS was observed for blends with w(2) >= 0.50. Blends with 0.40 <= w(2) <= 0.60 consisted of partially cocontinuous components; otherwise, particles of the minority component were dispersed in the continuous majority component. The compatibilizer enhanced interfacial adhesion so that no debonding of the components in the fractured blends was observed. The compliance and creep rate of the blends at room temperature decreased proportionally to the sPS fraction; a corresponding increase in the storage modulus (E') was observed in the 25-100 degrees C interval. However, E' (125 degrees C) noticeably declined with w(2) and thus showed that sPS did not improve the dimensional stability of the blends at elevated temperatures. The yield strength consistently grew with w(2), whereas the yield strain dropped markedly; blends with w(2) >= 0.60 were brittle, showing very low values of the ultimate properties. The stress at break, strain at break, and tensile energy to break displayed some local maxima at 0.25 <= w(2) <= 0.30, whereas the tensile impact strength steeply decreased. (c) 2005 Wiley Periodicals, Inc.