An apparatus for supplying a coolant in a throttle body includes a heating adaptor having a coolant passage therein in which coolant supplied thereto is circulated and discharged, a passage switching valve movably installed in a coupling hole provided at an inlet of the heating adaptor, and having a bypass passage in which the coolant circulated along the coolant passage is selectively blocked, and a drive unit connected to the passage switching valve for sliding the passage switching valve so that the coolant supplied to the heating adaptor is discharged along the bypass passage.