An apparatus and method for converting color data are provided. The method includes generating a CMYK color gamut extended from a CMY color gamut that consists of a cyan (C) colorant, a magenta (M) colorant, and a yellow (Y) colorant, by use of the CMY color gamut and a black (K) colorant; mapping input colors using the generated CMYK color gamut; converting color data of the mapped input colors to CMY data; and converting the CMY data to CMYK data. Accordingly, natural representation and printing of low-lightness colors and high-saturation colors can be attained.