In comparison to semi-crystalline polymers like polyethylene or polyamide, the poly(lactic acid) (PLA) has a very slow crystallization rate. The production of semi-crystalline molded parts is only possible if the material contains nucleating agents, or if the injection-molding process is significantly tailored to account for the slow crystallization kinetics. In this study investigations were done on the process – structure – properties behavior of PLA, focusing on the production of semi-crystalline molded parts without usage of nucleating agents. Three different types of PLA varying in their molecular architecture and melt-flow index were compared using differential scanning calorimetry DSC and polarized-light optical microscopy combined with hot-stage experiments. The influence of the thermal and rheological process conditions and the thermal treatment after processing on the morphology development and crystallinity were analyzed. It is shown that annealing after processing has big influence on the crystalline structure and crystallinity degree regarding to the samples which crystallized slowly inside the cavity during processing. The elongation at break and tensile strength decreased with increasing crystallinity.