We investigated the effects of addition of oleic acid (OA) on the stability of CsPbBr3 quantum dot (QD) dispersions in toluene during storage and light irradiation. Excess amounts of OA degraded the fluorescent perovskite CsPbBr3 QDs because of promoted crystal growth through dissolution and reprecipitation. In contrast, a suitable amount of OA (0.2 vol%) improved their photostability possibly due to re-adsorption of OA on the exposed CsPbBr3 crystal surface after the photoinduced desorption of OA.