Abstract：Single- and pauci-chain aggregate samples in amorphous state were prepared from aerosols of isotactic polystyrene (i-PS) in a concentration range of 1×10－3～2×10－5 g•mL－1 by the freeze-drying procedure. It was found that as the concentration decreases, the i-PS chain coils would be well separated in solution and the resulting intrachain entanglements may decrease, therefore, the amount of single- and pauci-chain coils, within collected particles obtained via the freeze-drying procedure, increases gradually. The results of freeze-drying samples by DSC indicated that the crystallization temperature shifts lower, the melting point and the crystallinity decrease as the solution concentration decreases. The samples prepared from 2×10－5 g•mL－1 solution are melt-crystallized at 468.3 K for 60 min, then single-chain single-crystal with an average volume of 1.5×104 nm3 was obtained. The crystal grain size was about 20 to 50 nm by the SEM micrograph. By means of the polarized optical microscopy (POM), the spherulite growth rates of i-PS single or pauci-chain congeries are calculated at various crystallization temperatures. With described by the theory of Hoffmann, the critical nucleation parameters of single-chain single-crystal of i-PS were calculated as follows: the fold surface free energy (σe) was 30.2 erg•cm－2; the lateral surface energy (σ) was 5.7 erg• cm－2 and the work of chain folding (q) was about 4.5×10－13 erg•molecule－1. Compared to the values reported in literatures, the results indicate that entanglements have a pronounced effect on the crystallization behavior of polymer.