The kinetics of the thermally induced solid-state polymerization (SSP) of nylon-6 were examined in both a fixed-bed reactor and a rotary reactor. Factors such as the regulator content, the reaction temperature and time, the particle size, the type and geometry of the nylon-6 prepolymer, the nitrogen gas flow rate, the water content of the nitrogen gas flow, and the polymerization process were studied. The results showed that the regulator content, the reaction temperature and time, and the particle size were the primary factors, and that the others were negligible. Moreover, the SSP rate and number-average molecular weight (M-n) increased with increasing reaction temperature and time and decreasing particle size. The SSP rate and M-n had maximum values with increasing regulator content in an experimental range of 0.03-0.07 wt %