Abstract: A staple magazine for stapler including an elongated outer casing, an elongated inner casing fixedly mounted inside the outer casing and defining with the outer casing two staple guide grooves, and a top cover plate covered on the outer casing, the guide grooves having different widths for enabling the staple magazine to carry staples/nails of different sizes, the top cover plate having a ridged top wall fitting ridged staples, one upright sidewall of the inner casing having a longitudinally extended protruded portion of smoothly arched cross section protruding toward the other upright sidewall of the inner casing and serving as a guide rail to work with one of the guide grooves for carrying U-nails.