A simple method for the direct determination of mercury in ethanol fuel samples diluted with water by cold vapor atomic absorption spectrometry (CV-AAS) is proposed. The chemical parameters (concentrations of NaBH4 and HCl) used for the Hg vapor generation for its measurement by CV-AAS were optimized. The calibration curve showed a linear response over the studied range (1-25 mu g L-1), with a correlation coefficient of 0.9999 and limits of detection and quantification of 0.05 and 0.17 mu g L-1 respectively. The relative standard deviations were lower than 3.5%. The accuracy of the method was estimated by applying the recovery test, and recovery values obtained were 84 and 106%. A sample throughput of 45 h(-1) was achieved. Simplicity and sensitivity are among the advantages offered by the proposed method.