Abstract Organic-inorganic hybrid perovskites, such as CH3NH3PbI3 and NH2CH=NH2PbI3, emerge as a new class of low-cost semiconductors that have the potential applications in high-efficiency photovoltaic cells, light emitting diodes, lasers, and sensors. However, hybrid perovskites can be easily degraded by H2O, O2, and light in ambient conditions. To improve the stability of hybrid perovskites, we carried out a comprehensive study including the degradation kinetics and surface modification by vapor-solid reactions for encapsulation. The degradation kinetics of perovskites were studied by using in situ methods. We found CH3NH3PbI3 perovskite degrades slowly at 85°C. This result indicates hybrid perovskites alone is not stable in the working conditions. We enhanced the stability of perovskites by surface modification through studying the surface reaction mechanism on perovskites. We found that by increasing the partial pressure of vapor reactants such as pyridine, the vapor-perovskite reactions will change from surface terminated reaction to bulk transformation reactions. A thin pin-hole free oxide barrier layer cannot only block H2O and O2 from meeting perovskites but also encapsulate the gas byproducts from the degradation reactions to stop the reversible degradation reaction. Atomic layer deposition (ALD) is a promising method to deposit a pinhole-free metal oxide barrier film onto perovskites. Although there are numerous reports in applying ALD on hybrid perovskites, the nucleation mechanism of ALD on these perovskites are poorly understood. Herein, we will present our findings about the atomic level surface reaction mechanism during ALD on perovskite-related substrates. Collectively, we are able to create a couple of new pathways to improve the stability of perovskite materials.