This study has been carried out to investigate the structural changes of poly(lactic acid) fibers, which may occur during the dyeing process. Four disperse dyes with long alkyl chains were used to demonstrate the effects of dyeing temperature on fiber structure. Polymer structure was studied using DSC and SAXS-WAXS techniques. It was found that dye uptake increased at temperatures above 70°C. The tested dyes did not show a distinct behavioral pattern. Poly(lactic acid) crystallinity increased from 53% to 60% after dyeing at 130°C. Double melting behavior was observed, suggesting the presence of two crystalline forms. This was refuted by SAXS-WAXS results. Melting behavior was investigated and the nature of the crystals was found to be independent of the dyebath temperature.