The purpose of this study is to achieve a better understanding of the influences of enzymatic and caustic pretreatments on the dying adsorption behavior of Lyocell yarns. The substantivity behavior, dyeing adsorption isotherms and their correlation between the equilibrium modeling and equilibrium isotherm parameters of the pre-treated Lyocell fibers have been studied. Although the conditions of each treatment were the same, changing the processing sequences caused substantially different modifications on the Lyocell fiber fine structure with consequent effect on dyeing behaviors. In general, pretreatment by caustic soda and/or enzyme can improve their dyeability of Lyocell fibers. The results of dyes adsorption show that for the same enzymatic treatment condition if the enzymatic treatment stage is applied before the caustic pre-treatment, the dyeability and sorption ability of small molecule dye on pre-treated Lyocell can be improved over that which can be obtained for caustic pre-treated yarn.