Recently, pigmented inks became popular for personal and office printers. They have advantages in waterfastness and lightfastness, but they have limitations on rub resistance. Therefore, new inks have been required to overcome this problem.Firstly, we investigate effects of additive in ink formulation. Secondly, pigments of hydrophobic surface are introduced. Finally, two pigments having different surface are applied for the optimum condition of additives for improving rub resistance, while maintaining optimum optical density.As the result, we found that the hydrophobic pigments increased the rub resistance, moreover, preserving optimum optical density. The result of this study will be valuable for overcoming the weak point of pigment based inks.