In an experiment on pressure-driven ion transport in nanopores of a zeolite, the anion concentration is varied in a broad range. As the anion concentration is relatively low, its influence on the ion transport pressure, which reflects the system free energy variation rate, is negligible. When the anion concentration is relatively high, it has a pronounced effect on the ion transport pressure, which should be attributed to the unique surface ion structure in the confining nanoenvironment. The testing data also indicate that the effective interfacial tension is highly dependent on the anion size. © 2009 American Institute of Physics.