Results of a study on the isothermal crystallization and thermal behavior of both uncured and hexamine-cured novolac/poly(ethylene oxide) (PEG) complexes are reported. The crystallization behavior of PEG in complexes is strongly influenced by factors such as composition, crystallization temperature, complexation, and crosslinking. The time dependence of the relative degree of crystallinity at high conversion deviated from the Avrami equation. The cured complexes exhibited an obvious two-stage crystallization (primary crystallization and crystal perfection), and this was more evident at higher crystallization temperature and high PEG-content. The addition of a noncrystallizable component into PEG caused a depression of both the overall crystallization rate and the melting temperature. In general, complexation and curing resulted in an increase in the overall crystallization rate. Complexation and curing are beneficial to the nucleation of PEG. Additionally, curing led to changes of the nucleation mechanism. Experimental data on the overall kinetic rate constant K-n were analyzed by means of the nucleation and crystal growth theory. For uncured complexes, the surface free energy of folding, sigma(e), increased with increasing novolac content, whereas for cured complexes, sigma(e) displayed a maximum with the variation of composition.