A new method has been developed for the determination of silver ion based on separation and preconcentration with a microcolumn packed with multiwalled carbon nanotubes (MWNTs) prior to its determination by flame atomic absorption spectrometry (FAAS). The optimum experimental parameters for separation and preconcentration of silver, 'such as sample pH, sample flow rate and volume, elution conditions, and interfering ions, have been investigated. Silver ion can be quantitatively retained by MWNTs in the pH range 7 similar to 9, and then eluted completely with 1.0 M HNO3. The detection limit of this method for Ag was 0.60 ng mL(-1), and the relative standard deviation (RSD) was 3.8% at the 10 ng mL(-1) Ag level. The method has been successfully applied for the determination of trace silver in geological and water samples.