To obtain the subject dye, containing a disperse dye having a specific molecular weight as an active component, excellent in exhausting properties and capable of providing a dyed or a printed product excellent in wet color fastness.

This disperse dye for a high-speed spun polyester fiber comprises a disperse dye having ≥400, preferably 405-660 molecular weight in order to dye or print the polyester fiber spun at a speed as high as ≥6000m/min (and its blended spun or a combined filament product, etc.) as an active component. The coloring of wastewater after the dyeing and printing can remarkably be reduced.