A deflectable probe for use in a thermometer. The deflectable probe is constituted by a bendable probe body and a hollow tip member secured thereto. Furthermore, a deflectable member includes a main portion disposed in the bendable probe body. When the bendable probe body is subjected to a force, deformation of the main portion occurs. In particular, the deformation cannot be undone by a return force from the bendable probe body when the applied force is removed, so that the bendable probe body is sustained in a bent form. A space is formed between the hollow pipe and the main portion of the deflectable member for deformation of the main portion to prevent the deflectable member being easily pushed into the hollow cavity and avoid the lead wires being easily cut off.