High-resolution solid-state 1 5 N and 1 3 C NMR and dynamic mechanical measurements were carried out for solution grown crystals of the α- and γ-forms of nylon-6 to understand the relation between segmental mobility including interchain interactions and ductility of polyamides. The ductility, in the temperature range of 100-180 o C, was lower for the α-crystals than for γ-crystals. 1 5 N chemical shift revealed that the hydrogen bonding was stronger for the γ-crystals than for α-crystals. In addition, lower mobility of NH group in the γ-crystals than in α-crystals was shown by 1 5 NT 1 results. The results suggest that the ductility of nylon-6 could not be simply related to the strength of hydrogen bonding. Highly crystalline films of aggregates of solution grown α-crystals and γ-crystals showed no crystalline relaxation in the temperature dependence of dynamic mechanical loss factor, suggesting an existence of strong intermolecular interactions in the crystalline regions although 1 3 CT 1 data indicated that the mobility of methylene units was higher in the γ-crystals than in α-crystals. Information on the large-scale chain dynamics in the crystalline regions might be necessary to understand the low ductility of polyamides.