A method for the determination of Cu, Zn, Fe, Ni and Cd in geological samples by flame atomic absorption spectrophotometry (FAAS) after preconcentrating by Aspergillus niger immobilized on sepiolite has been developed. The column adsorption method was used for the preconcentration studies. Effects of pH, amount of adsorbent, elution solution, flow rate and interfering ions on the recovery of the analytes have been investigated. Recoveries of Cu, Zn, Fe, Ni and Cd on Aspergillus niger immobilized sepiolite were 98.01+/-0.06%, 98.8+/-0.5%, 98.0+/-0.4%, 96.4+/-0.8% and 94.8+/-0.6% at 95% confidence level, respectively. The breakthrough capacity of the adsorbent was found as 0.093, 0.078, 0.067, 0.085 and 0.102 mmol/g for Cu, Zn, Fe, Ni and Cd, respectively. The proposed method was applied to the determination of trace metals in geological samples, such as AGV-1, JG-1a and Wismuterz II. Trace metals have been determined with about 5% relative error.