Melt treatment of A357 alloy including purification (i.e. degassing and inclusion removal), grain refinement and modification of eutectic silicon was performed by the flux injection process in a resistance furnace. The microstructure and tensile properties of the alloy were examined by optical microscopy, scanning electron microscopy and tensile test, and compared to those of the same alloy treated by conventional methods. The results indicate that by selecting suitable fluxes and optimizing injection parameters, this process could realize the melt treatment of A357 alloy, and may be superior to conventional methods. The alloy treated by this process possesses the strength comparable to that treated by conventional methods, but shows higher elongation. The advantage of this process over conventional methods is discussed according to the powder injection metallurgy theory.