An apparatus for aligning a wafer is provided, which normally senses a flat zone of the wafer by sensors regardless of an external light so that the wafer is aligned in a set mode, in order to increase or maximize production yield. A body has all kinds of drivers. An orient chuck is provided to protrude to an upper portion of the body for rotating the wafer; a guide plate ascending and descending to slide a circumference surface of the wafer so that a center of the wafer is located on the orient chuck. A plurality of sensors sense a flat zone of the wafer being rotated on the orient chuck. A wafer carrier cassette is formed at an upper portion of the orient chuck in order to load the wafer aligned in one direction by the sensors and the orient chuck, and is supported by a plurality of frames formed at respective corners of the body. A panel wall encloses a circumference of the frame at peripheries of the orient chuck and sensors between the wafer carrier cassette and the body, and intercepts an external light to be incident to the sensors.