A radio frequency (RF) application circuit is provided. In the RF application circuit, a pair of bipolar junction transistors (BJTs), instead of N-channel metal-oxide-semiconductor (NMOS) transistors, is composed of a switch-block operated in a reversion saturation region. The RF application circuit is used to serve as either an oscillator or a band pass amplifier according to the circuit characteristic of an active circuit. Thereby, not only the function of the conventional NMOS transistor served as a switch can be achieved by the switch-block, but also the element size, turned-on resistance value and turned-off parasitic capacitance value of the switch-block, and the power consumption of the RF application circuit thereof can be reduced. Thus, the resolution of the capacitance unit in a LC resonance circuit and the performance of the RF application circuit thereof can be promoted.