In disperse dyeing of polyester fibers, reduction clearing is conducted to improve the wet fastness of the dyed material. However, in the case of disperse dyeing of cellulose diacetate fabrics, when reduction clearing is conducted, the acetyl groups in cellulose acetate fibers may be alkali-hydrolyzed, which leads to a deterioration of their characteristic properties. Therefore, the dyed acetate fabrics are usually after-treated with a soaping agent at a relatively low temperature for better wet fastness, although it fails to meet the customer demands. In this study, high-washable phthalimide-based azo disperse dyes were synthesized, and their dyeing and fastness properties on cellulose diacetate fabrics were investigated. In particular, conventional 4-aminoazobenzene dyes containing a nitro group at the 4-position were synthesized to compare their fastness properties on cellulose acetate with those of phthalimide-based azo disperse dyes.