Abstract: A series of dichlorobenzidine disazo yellow pigments and their synergistic mixtures are synthesized through tetrazo-coupling reaction. Experimental results show that their properties, e. g., color strength, brightness, brilliancy and particle size of the synergistic pigment mixtures, as compared with that of the single pigments and mechanically mixed pigments, are modified. The X-ray diffracteon analysis and electronmicroscopic analysis indicate that the formation of substitution solid solution is the cause for the synergistic effect of those modified pigments.