Inorganic lead halide perovskite nanocrystals (NCs) have recently become one of the research topics for optoelectronic applications due to their excellent photophysical properties. Despite their notable thermal stability over organic-inorganic halide perovskites, CsPbI3 NCs suffer from the phase instability of α-CsPbI3 phase at room temperature and under ambient conditions. Here, the effects of 4-Hydroxybenzoic acid (4-HBA) as an additive to standard oleic acid – oleylamine pair on the stability and optical properties of CsPbI3 perovskite NCs are discussed. 4-HBA addition into perovskite NC systems causes a compressive strain on perovskite lattice, which leads to the formation of a mixed phase α- and γ-CsPbI3 phases while pristine perovskite has α-CsPbI3 phase. Time-dependent stability of the perovskite NCs was tested under an ethanol (EtOH) medium. After EtOH exposure of the perovskite NCs, CsPbI3 NCs transformed to non-perovskite phase in 1 h while 4-HBA added CsPbI3 NCs still have perovskite phase after 48 h. In addition to the improved optical properties of the perovskite NCs, 4-HBA addition remarkably improves CsPbI3 perovskite stability.