An electric rotation device for an automobile seat disclosed in the present invention includes a rotary support, a rotary disc, a fixed disc, a platen, an upper ball assembly, a lower ball assembly, a driving motor assembly, and a semicircular rack. A center of the semicircular rack coincides with a center of rotation of the rotary support. The semicircular rack is meshed with the driving gear. The driving gear in the driving motor assembly is configured to drive, by using the semicircular rack, the rotary support to perform reciprocating rotation in a range of 0-180°. A special-shaped tooth configured to prevent the driving gear from rotating out of the semicircular rack is disposed at each of extreme positions on two ends of teeth in the semicircular rack, so that the driving gear is gradually snapped with the special-shaped teeth to stop further rotation when rotating to the extreme positions on the two ends of the semicircular rack. The present invention has advantages such as an increased strength, reduced costs, and elimination of a gap between extreme positions. In addition, a wire harness of a seat is prevented from being broken as a result of unlimited rotation.