PURPOSE: To enable the dyeing of a diacetate fiber in high color density at a low temperature and high build-up ratio by carrying out the dip dyeing of a diacetate fiber in a dyeing bath produced by mixing a disperse dye with a specific compound and dispersing the obtained liquid mixture in a dyeing solution.

CONSTITUTION: A disperse dye is mixed with 1,3-dimethyl-2-imidazolidinone and then incorporated with N,N-dimethylformamide and the three components are thoroughly mixed at ratios of 1: (4-80):(1-200). The liquid mixture is dispersed in a dyeing bath and a diacetate fiber is dipped in the dyeing bath having excellent dispersed state and subjected to dip dyeing at a low temperature (about 90°C) to obtain the objective fiber dyed in dense color in high build-up ratio. The selectable range of the hue can be expanded and a dyed product having excellent fastness can be produced by the dyeing method.