In this paper, a successive heating and cooling protocol was designed to investigate the self-nucleation behavior of poly(lactic acid), PLA. The main objective of this investigation was to study the efficiency of the alpha and alpha' crystalline modifications of PLA. This was carried out by comparing crystallization temperatures upon cooling after self-nucleation of samples previously crystallized at various isothermal temperatures ranging from 80 to 130 degrees C. During heating to the partial melting range, three different mechanisms were observed for crystallized samples. For samples crystallized below 100 degrees C, an exothermic peak was detected prior the main melting peak which is ascribed to the alpha'-alpha solid-state transition. For samples crystallized between 100 and 120 degrees C, a melt recrystallization mechanism was observed. Finally, for samples crystallized above 120 degrees C, only melting of the alpha phase was detected. Upon cooling after partial melting, it was found that samples comprising a mixture of alpha and alpha' exhibited the highest crystallization temperature, the highest nuclei density, and the smallest spherulite size. Moreover, it was observed that samples that were isothermally crystallized between 100 and 120 degrees C, heated up to partial melting, and then cooled back to room temperature exhibited two peculiar crystallization peaks at 100 and 120 degrees C. This phenomenon was ascribed to the formation of alpha and alpha' crystalline phases as revealed by X-ray diffraction. In addition, by slightly changing the temperature within the self-nucleation temperature range, a change of the proportion of each peak was observed.