For ink-jet color inks used for the well-known printers, taking Canon, EPSON, HEWLETT PACKARD and LEXMARK as samples, transmittances of the ink solutions were determined, and then the chromaticity analyses were made, in order to calculate the tristimulus values and the chromatic coordinate of each color sample. Also, the gamuts, chroma values, dominant wavelengths and complementary wavelengths were obtained by using the chromatic method for the samples. In this paper, an empirical formula was suggested for the relationship between the complementary wavelengths of the three primary colors: lambda compl, M approximately equal 10/9 (lambda compl, Y) + 10 and lambda compl, M approximately equal 10/9 (lambda compl, Y) - 20. It was found that the empirical formula is well suited for matching the complementary wavelengths of the three primary colors for ink sets of the samples studied.