A variable deflector apparatus for a side step of a vehicle may include a drive device, a side deflector operated by power transmitted from the drive device, the side deflector configured to be received in the side step when the side deflector is not deployed and to be perpendicularly drawn out downwards from the side step when the side deflector is deployed, thus improving aerodynamic performance of the vehicle, and a front deflector connecting a front end of the side step with a front end of the side deflector, the front deflector being kept folded when the side deflector is not deployed and configured to be unfolded to cover a lower portion of the front end of the side step when the side deflector is deployed, thus improving the aerodynamic performance of the vehicle.