Poly(trimethylene terephthalate) (PTT)/glass-fiber composites were investigated in the presence of nucleating agents. Sodium ionomer of poly(ethylene-co-methacrylic acid), disodium p-phenolsulfonate, and disodium p-hydroxybenzoate were adopted as the nucleating agents. Modified composites were systematically studied, including crystallization behaviors and both mechanical and melt viscosities, and were compared with PTT and poly(butylene terephthalate) composites without nucleating agents. All three sodium salts were found to be effective in accelerating the crystallization, but showed quite different characteristics upon closer investigation. Their efficacy at promoting the crystallization rates ranked in the order of disodium p-hydroxybenzoate, disodium p-phenoisulfonate, and sodium ionomer. Besides the accelerating effects, sodium ionomer increased the melt viscosity and disodium p-phenolsulfonate showed nearly no influence on the melt viscosity of the PTT composite, whereas disodium p-hydroxybenzoate resulted in significant polymer decomposition. High crystallization rates and good mechanical properties were successfully obtained simultaneously, by suitably using p-phenolsulfonate or a combination of the other two agents. (c) 2005 Wiley Periodicals, Inc.