Al–17 mass%Si–4.5 mass%Cu–0.5 mass%Mg rapidly solidified powder metallurgy (RSP) alloy was prepared by hot extrusion method. High temperature tensile property of the alloy was investigated in the temperature range from 400 to 540°C. Typical superplastic behavior was observed at 500 and 520°C. The value of the maximum tensile elongation of the alloy tested at 500°C was about 380% with an initial strain rate of 10⁻²s⁻¹. At 520°C, partial melting phenomena by solute segregation at some grain boundaries were induced, and the maximum elongation of about 390% was obtained at higher initial strain rate than the case at 500°C of 10⁻¹s⁻¹. The superplastic behavior at both the temperatures may be based on grain boundary sliding and accommodation mechanism. At 520°C, the liquid phase at grain boundaries may play the role of an accommodation helper, absorbing dislocations and relieving the stress concentration due to sliding.