Disperse dye structure affects the dyeability of poly (lactic acid) (PLA) fiber due to the low dyeing temperature and the short dyeing time. Thus, the dye uptake value of PLA fiber is low for some disperse dyes and needs to be improved. In this study, the dyeability of PLA fiber is improved with the addition of synthesized octa (aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) nanoparticle during the melt spinning process. The effects of dyeing conditions including dyeing temperature and time, OAP-POSS concentration, disperse dye types, and concentrations are investigated on the dyeability properties of PLA fiber samples. The tensile, thermal, and morphological properties of the fiber samples are also characterized by tensile testing, differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It is concluded that the percent crystallinity and the tensile strength of pure PLA fiber decrease as the added amount of OAP-POSS increases. According to the dyeing results, OAP-POSS, which behaves as a good sorbent for the disperse dyes used in this study, greatly improves the dyeability of PLA fiber, especially for disperse dyes with low dye uptake values.