Abstract: A direct heat rotary dryer having a single-wall rotating cylinder (10), an axial duct (20) connected to a hot-air source to axially extend inside the cylinder, a plurality of radial ducts (21) branched from the axial duct, each radial duct extending slantingly downwardly near to the inner surface of the cylinder and being formed with a nozzle, whereby hot air flows through materials so that an efficient heat-transfer is made between the materials and the hot air. A plurality of pins (25) are provided on the inner surface of the cylinder (10) along a circle between two adjacent radial ducts (21) to prevent materials from forming lumps.