Catalytic properties of the 75 nm and 0.8 mu m-sized SAPO-34 crystals on acetone-to-olefins (ATO) reaction were compared. The 75 nm-sized crystals (nanocrystals) showed longer catalyst lifetime than 0.8 mu m-sized crystals, and products selectivity was similar for the two SAPO-34 catalysts, as is the case in methanol-to-olefins (MTO) and dimethyleter-to-olefins (DTO) reactions. The reaction site of ATO reaction over SAPO-34 was studied using coke-deposited SAPO-34 as catalysts whose pores are deactivated through the DTO reaction. The reason for longer catalyst lifetime of the nanocrystals in the ATO reaction must be a large surface area of the SAPO-34 nanocrystals, unlike in the case of the MTO and DTO reactions.