Two new synergists, PY74ACA-1 and PY74ACA-2, were prepared for pigment dispersion in water-base ink. Synergists interact with pigments and dispersants to increase the dispersion degree of the pigment particles and it stabilizes the pigment particles in the pigment dispersion state. 6-bromohexanoic acid was attached to pigment-74 as hydrophilic functional group. The original pigments showed very low solubility in water and organic solvents such as DMSO, DMF and methanol. Two synergists were found to have higher solubility than pigment, and especially PY74ACA-2 shows better solubility than PY74ACA-1. These results indicate that 6-bromohexanoic acid prevents pigment aggregation well, and increases the solubility in water as the increased polarity. Two synergists being applied to pigment inks are expected to improve the dispersion properties and storage stability of pigment inks.