The dyeability of C. I. Disperse Violet 1 on polyester fiber in alkance including a small amount of water was investigated. Up to 1% of water in alkanes the dye uptakes were increased rapidly. The dyeing transition temperature of the polyester fiber in alkanes with 1% of water was $86.5^circ{C}$ that is lower by $11^circ{C}$ than $97.5^circ{C}$ in alkanes only. This means that water plasticizes the polyester fiber, and that dyes begin to penetrate the polyester fiber at lower temperature. Addition of trichloromethane which is known as a strong plasticizer on polyester fiber, in alkanes, increased the dye uptakes of C. I. Disperse Violet 1 on polyester fiber at $100^circ{C}$, but the dyeing transition temperature was lower by $3^circ{C}$ than in alkanes only.