Superplastic behavior of a duplex stainless steel has been studied at 1223 K (950 degreesC) and 1253 K (980 degreesC) for initial strain-rates ranging from 2x10(-4) s(-1) to 8x10(-3) s(-1). In the given range of temperature, it was observed that the elongation increased as the strain rate decreased. The best superplastic conditions were obtained at 1253 K where the samples presented homogeneous deformation along the gage length. Under this temperature the maximum elongation (900%) was obtained for an initial strain-rate of 4x10(-4) s(-1). Those results were also confirmed by determination of the strain-rate sensitivity coefficient, m, which presented the highest value at 1253 K and dearly increased with decreasing strain-rate, Microstructure studies and previous information about the amount of cavities suggest that the deformation process occurs by a superplastic grain boundary sliding mechanism.