A disposable toothbrush with a built-in toothpaste applicator mechanism, the toothbrush mainly comprising a multiplicity of bristles, a plurality of apertures located between the bristles, a hollow compartment for containing a quantity of toothpaste, a bore connecting the apertures and the hollow compartment, a flexible locking member, and a plunger with a head, a base and a stem. The head of the plunger is dimensioned to achieve a substantially gapless interface inside the hollow compartment for pushing the toothpaste into the bore and out from the apertures. The locking member is secured over the stem of plunger for preventing it from being accidentally pushed into the hollow compartment before using the toothbrush. In order to use the toothbrush, first the locking member is removed. Then the plunger is pushed into the hollow compartment to extract the toothpaste out from the plurality of apertures and on to the bristles.