A pneumatic tool (610) and a muffler assembly (600) therefor, for quieting the operation of the pneumatic tool, are disclosed. In one embodiment, the muffler assembly (600) is slidably disposed within the exhaust passage (616) and includes a tube member (602) having a proximal flange (604), an intermediate tubular portion (606) with apertures (608), and a distal receptacle (620). The tubular portion may include a blocking plate (618) therein. A porous, sound-deadening panel (622) is disposed about the tubular portion, and a diffuser panel (630) is disposed in the distal receptacle. A perforated end cap (624) holds the muffler assembly in place. In operation, the exhaust enters the tube member, is directed transversely through apertures in the tubular portion and through the porous panel, then back into the distal portion of the tube member, through the diffuser panel, and exits through the end cap.