Abstract: Mordant dyeing is the conventional method for the dyeing of gardenia blue on wool because of the low affinity between dyes and wool fiber. However, the usage of mordant dyeing could result in the environmental pollutions easily. Chitosan, which is a natural biodegradable polymer, could be used to pretreat with wool fiber. The dyeing mechanism of gardenia blue on wool fiber pretreated with chitosan was studied by exploring the dyeing rate and kinetic model of dyes on wool fiber. The results indicated that the dyeing rate and dyeing equilibrium adsorption capacity of dyes on chitosan-pretreated wool fiber were higher than that of dyes on untreated wool fiber. In addition, the adsorption process of gardenia blue on both chitosan-pretreated and untreated wool fiber was in accord with the pseudo-second-order dynamic model, indicating that the dyeing of gardenia blue on chitosan-pretreated wool fiber was mainly chemical absorption process.