Commercial montmorillonite Cloisite^® 30B (C30B) was activated by hexamethylenediisocyanate (HDI), isophorone diisocyanate (IPDI) and toluene diisocyanate (TDI), and then terminated and polymerized by caprolactam (CLA). Nine types of modified C30B were prepared, and their structures were characterized by FT-IR, SAXS, TGA to identify the optimum modified C30B. The effects of C30B and modified C30B on the crystallization properties, mechanical properties and water absorption of nylon 6(PA6) were studied. Both C30B and modified C30B can improve the mechanical strength and crystallization rate of PA6, and promote a polymorphic transformation. Furthermore, the uniform dispersion of the montmorillonite and the increased crystallinity reduced the water absorption of the composite. Compared with PA6/C30B (mass ratio 199/1), the elastic modulus of PA6/C30B-TDI (mass ratio 199/1) composite increased by about 12.6%, the yield strength increased by about 9.2%, and the elongation at break increased by about 72.6%, showing that using C30B-TDI results in more effective modification of the mechanical properties of PA6.