High-quality SSZ-13 membranes were synthesized on 200 nm asymmetric a-alumina supports via a single hydrothermal secondary growth. Single CO2, N-2 and CH4 permeances and mixed gas separations in CO2/CH4 and N-2/CH4 binary mixtures through SSZ-13 membranes were measured. Synthesis conditions such as membrane substrate, gel composition and membrane calcination were modified. The best SSZ-13 membrane displayed N-2 and CO2 permeance as high as 8.9 x 10(-8) mol/(m(2)sPa) and 5.6 x 10(-7) mol/(m(2)sPa) and N-2/CH4 and CO2/CH4 selectivities of 10 and 56.5 for equimolar N-2/CH4 and CO2/CH4 gas mixtures at 298 K and 0.2 MPa feed pressure, respectively. Nitrogen permeance of current SSZ-13 membrane in the mixture was 3.7 times higher than that of our previous SSZ-13 membrane. The membrane synthesis was reproducible. Temperature and pressure dependences of separation performance in the two binary mixtures were also discussed. Single CO2, N-2 and CH4 permeances dependent of pressure were predicted by the Maxwell-Stefan diffusion model and the predicted values were fitted well with the measured ones. The stability of SSZ-13 membrane in the wet mixture was investigated. The current SSZ-13 membrane has excellent potentials for CO2 and N-2 removals from natural gas.