Ma Jun (fl.

220–265), style name Deheng, was a Chinese mechanical engineer and government official during the Three Kingdoms era of China.

His most notable invention is that of the South Pointing Chariot, a directional compass vehicle which actually has no magnetic function, but is operated by use of differential gears (which applies equal amount of torque to driving wheels rotating at different speeds).

It is because of this revolutionary device (and other achievements) that Ma Jun is known as one of the most brilliant mechanical engineers and inventors of his day (alongside Zhang Heng of the earlier Eastern Han Dynasty).

The device will be reinvented by many after Ma Jun, including the astronomer and mathematician Zu Chongzhi (429-500 CE).

In the later medieval dynastic periods, Ma Jun's South Pointing Chariot will be combined in a single device with the distance-measuring odometer.