The sorption thermodynamics and kinetics of disperse dyes on polylactic acid (PLA) fibers were investigated. PLA is crucial for a sustainable textile industry. However, the low dye exhaustion limits the textile application of PLA fibers. The basic dyeing parameters have been determined to provide an in-depth understanding of dyeing behavior. The weak sorption affinities were attributed to the weak dye-fiber interaction and favorable chemical potential of dyes in solvent. Enthalpy-entropy compensation effect also played a role in weak sorption. The interplay of dye structure and enthalpy, entropy changes was rationalized using molecular surface area and rotatable bonds. The conformation constraint strategy was proposed to overcome weak sorption affinity problem by lowering the entropy penalty. Temperature dependence of diffusion coefficients was well reproduced using molecular collision based diffusion model. The activation energies of diffusion have been correlated with molecular volumes of dyes.