A methodology to control miscibility and crystallinity of melt blend films of nylon 6 and poly(m-xylene adipamide) is discussed based on the results of differential scanning calorimetry. The blend film was partially miscible, i.e. miscible in the amorphous phase, as evidenced by (1) two crystallization temperatures and two melting temperatures that interacted with one other and (2) a negative Flory-Huggins interaction parameter, chi. However, the miscibility was further enhanced by ageing the blend film at 275 degrees C, which was due to amide exchange reaction. This miscibility enhancement was studied as a function of the ageing time, tau.