Superplastic behavior in Si₃N₄ particulate reinforced 606lAl matrix composite has been investigated in a constant strain rate tension test. The particulate composite was processed with hot extrusion at 773K with a reduction ratio of 100, and the as-extruded composite was tested at 818K. As a result, the particulate reinforced composite showed small elongation of 50% at low strain rate of 10^-4s^-1, however, total elongation increased with strain rate, and the composite showed large elongations of more than 400% at high strain rates of 10^-1-10⁰s^-1. The composite showed low m value of 0.1 at less than 10^-2s^-1, which corresponds to low elongation, however, showed high m values of more than 0.3 at more than 10^-1s^-1. The grains of the composite after annealing at 818K were less than 3μm and subgrain structure was observed in the grains. Grain boundary sliding pattern was observed on the surface of the specimen deformed superplastically. Superplastic deformation is probably due to the grain boundary sliding.