We discussed some kinds of additives for inkjet ink to improve ozone fastness of a print image. Test patches were printed by an inkjet printer using water base ink containing the additive, water soluble dye, glycerol, and some penetrants which are inactive to ozone. The ozone concentration of exposure test was 26ppm. We quantified hue change between initial print and the one exposed by ozone. First of all, some additives such as benzotriazole and amine, which are known to be effective on improving ozone fastness, and amino acid, which is known to improve dark stability of images, are examined for Cu phthalocyanine dye. We found that amino acid type compounds were more effective on ozone fastness. Next, we examined carboxylate salts and a quaternary ammonium compound to understand the effect of carboxylic group and amino group on ozone fastness. After the examination on many kinds of amine salts of carboxylic acid, the amine salt of low pKa carboxylic acid was found effective on ozone fastness. The mechanism of low pKa carboxylic acid was supposed that when the amine had a counter ion of low pKa acid, it could transfer the lone pair electron to ozone molecule easily. We examined the same additives for azoic dye, and found that the amine salts of carboxylic acid were effective on ozone fastness.