A motherboard testing apparatus for testing a motherboard by subjecting it to sequential power-on and power-off modes includes a control module, a switch module and a display module. The control module stores power-on and power-off number of times and outputs control signals accordingly. The switch module provides a first voltage to the motherboard according to the control signals. The switch module includes a photocoupler and a delay. The photocoupler includes an LED and a phototransistor. The delay includes a winding element and a switch element. The display module displays the time periods and the number of times the motherboard abnormally power-on and power-off. The LED receives the control signals. The phototransistor turns on when the LED emits light. The winding element is powered up and closes the switch element. The switch element outputs the first voltage.