The influence of the incorporation of nanoparticles (Na+ and organo-modified montmorillonites) in polyamide 6 (PA6) on the amorphous and crystalline fractions was investigated. Nanocomposites were prepared by a two-step melt-blending. The dispersion state of the nanoplatelets was analysed by transmission electron microscopy and rheology. The amorphous and crystalline fractions can be described by a three-phase model where the amorphous fraction is divided into mobile (MAF) and rigid (RAF) amorphous fractions. The contents of MAF, RAF and crystalline fraction were investigated by differential scanning calorimetry measurements and by dynamical mechanical analysis. In this work, the different phases were studied as a function of the nanoplatelet dispersion degree (the affinity between the organoclay and PA6 matrix). It was shown that the incorporation of nanoparticles increased the RAF content which is directly related to the dispersion state. Exfoliation leads to an increase of RAF content.