A button-type tester for a LED lamp string includes: a housing formed with a chamber to accommodate a power source component; a circuit board disposed in the chamber, and including a control circuit and a contact switch, the control circuit being connected to the power source component and being operable to activate and deactivate the lamp string, the contact switch being connected to and being operable to enable and disable operation of the control circuit; a cap mounted on the housing and permitting access into the chamber; and a cover plate movably disposed in the chamber between the cap and the contact switch and accessible via the cap for actuating the contact switch so as to control operation of the control circuit.