A fast, sensitive, and on-line hydride generation method using ultrasonic nebulizer was applied for the determination of Sb(III) and Sb(V) by inductively coupled plasma-optical emission spectrometry (ICP-OES). In the proposed technique, an ultrasonic nebulizer was used for on-line and direct hydride generation as well as for sample introduction into the ICP-OES. The Sb(III) could be selectively determined by introducing the mixture of sample and reductant solutions directly into the ultrasonic nebulizer. The concentration of Sb(V) was calculated by the difference between total Sb and Sb(III). The effects of different experimental parameters on the performance of the method were studied. Under the optimum conditions, the limits of detection 0.04 and 0.14 ng mL−1 were obtained for Sb(III) and Sb(V), respectively. The precision of the method, evaluated as the relative standard deviation obtained by analyzing a series of ten replicates, was below 1.7% for both elements. The developed procedure was applied for the determination of antimony species in various water samples.