The catalytic properties of SAPO-34 nanocrystals (crystal size: 75 nm) on methanol-to-olefins (MTO) and dimethylether-to-olefins (DTO) reactions were compared with those of SAPO-34 (crystal size: 800 nm). The SAPO-34 nanocrystals showed a longer catalyst lifetime in both the reactions than 800 nm-sized SAPO-34. The rate of catalyst deactivation of SAPO-34 was similar for both the MTO and DTO reactions indicating that the reaction of MeOH to DME and the diffusion of MeOH and DME into the SAPO-34 nanocrystals are fast and are not a rate limiting process. A possible reason for the long catalyst lifetime of the SAPO-34 nanocrystals is a short residence time in a crystal for the produced hydrocarbons because of a shorter diffusion length.