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This study presents the development of a novelty on-line preconcentration method for inorganic molybdenum by flow injection solid phase extraction associated to inductively coupled plasma-optical emission spectrometry with ultrasonic nebulization (SPE-USN-ICP OES). This was made employing a minicolumn filled with ethyl vinyl acetate turnings as adsorbent material. This system was applied to the on-line preconcentration and determination of molybdenum in water samples with good sensibility and reproducibility; and Mo could be retained onto the minicolumn without further complexation. The time required for the preconcentration of 20 mL of sample, injection/data acquiring and conditioning was about 5.0 min, resulting in a sample throughput of 12 samples per hour. A 300-fold total enhancement factor for this sample volume was obtained with respect to the molybdenum determination by ICP OES without preconcentration. The precision for six replicate measurements of a solution containing 20 µg Mo L-1 was 3.5% relative standard deviation, calculated with the peak heights. The limit of detection (3s) was 0.04 µg L-1. This method was successfully applied to trace molybdenum determination in drinking water samples and in a certified reference material (Metals in Natural Waters, NIST CRM 1643e).