The recrystallization process of poly(N-methyldodecano-12-lactam) MPA has been studied by differential scanning calorimetry (DSC), wide- and small-angle X-ray scattering (WAXS, SAXS) and Raman spectroscopy. During this irreversible process, the primary crystalline structure with a melting temperature of about 324 K is transformed to the higher-ordered final structure melting at 335 K. Isothermal recrystallization has an optimum at 327-329 K. During recrystallisation, no change in crystalline modification takes place; however, crystallinity is increased from 30 to 35% (by WAXS) and the long period rises from 10.0 to 11.2 nm. The MPA sample recrystallized at 327 K and relaxed at laboratory temperature shows the melting point of 338.8 K. Crystallization/recrystallization of MPA is a diffusion-controlled kinetic process dependent on molecular weight and the rate of temperature changes. On the molecular level, the crystallization/recrystallization processes taking place in MPA can be interpreted as being directed by two conformational transitions in MPA molecules, namely the trans/cis transition on the C-N bond and the gauche/trans transition of the C-C sequences.