An extension bar with built-in light includes an elongate body having an open first end and an engaging recess in a second end of the elongate body. A switch member with a first conductive member extends through a transverse hole of the elongate body. A carrier is received in the engaging recess and a second conductive member is connected to the carrier. A power supply unit and a light bulb are received in the passage. The first end of the second conductive member is moved to contact the power supply unit to activate the light bulb when a conductive hand tool is inserted into the engaging recess. The light bulb is also activated when rotating the switch member to contact directly the first conductive member, the second conductive member and the power supply unit.
