Improving the hydrothermal stability of zeolites promises attractive benefits for catalytic applications, especially in the case of nanosized zeolite. In the present study, a two-stage synthetic method, conducted at low (95 °C) and high (210 °C) temperatures sequentially, was developed to prepare nanosized SSZ-13 zeolite with enhanced hydrothermal stability. The crystal size was tuned within 50–300 nm by simply controlling the period in either stage. In addition, compared with the microsized counterparts, the nanosized SSZ-13 zeolite showed remarkably enhanced hydrothermal stability with exhibiting equivalent catalytic performance in the selective catalytic reduction of NO_x by ammonia (NH₃-SCR). The improved hydrothermal stability of nanosized zeolite was due to the structural healing by the high temperature treatment.