A process for producing a colorant comprises the step of mixing a coloring material and a block copolymer in a flow channel of a microreactor to obtain a dispersion comprising a colorant as a dispersoid. The flow-mixing channel may have a cross-sectional area of not less than 0.5 mm.sup.2, and the ratio of the total cross-sectional areas of flow channels connected with the flow-mixing channel to the cross-sectional area of the flow-mixing channel ranges from 0.01 to 0.1, and a rectangular cross-section having a ratio of a flow channel depth to a flow channel width of not less than 0.5.
