With trimesinic acid as a molecular weight regulator, the hydrolytic polymerization Of epsilon -caprolactam was carried out, and nylon-6 or polyamide-6 with three-branched chains was obtained. Through a systematic study of the effects of conditions such as the reaction time and concentration of trimesinic acid on the polymerization, we found that the conversion of caprolactam was almost insensitive to the initial concentrations of the regulators, but the relative viscosity of the polymer decreased with increasing trimesinic acid. Characterization investigations showed that differential scanning calorimetry curves changed from a single peak for normal nylon-6 to one main peak and one shoulder or one small peak for the branched polymer; the melting point of the star-shaped nylon-6 decreased with an increasing amount of trimesinic acid, whereas its crystallization temperature was higher than that of linear-chain nylon-6. A wide-angle X-ray diffraction study indicated that the crystal structure of the starshaped nylon-6 still belonged to the a form, and the crystallizability of the branched polymer with an elevated amount of trimesinic acid during polymerization did not seem to be weakened; the characteristic absorption of infrared spectra provided indirect evidence for the existence of branched chains in the polymer. Moreover, the mechanical properties of star-shaped nylon-6 and linear-chain nylon-6 were compared.