An oscillation circuit including a first transistor, a second transistor, a current source, a first inverter, and an impedance unit is disclosed. The first transistor has a first source receiving a first operation voltage, a first drain, and a first gate coupled to the first drain. The second transistor has a second source receiving the first operation voltage, a second drain, and a second gate coupled to the first gate. The current source is coupled between the first drain and a grounding voltage. The first inverter generates an oscillation signal and has a first input terminal, a first output terminal, and a first power terminal coupled to the second drain. The impedance unit is coupled between the first input terminal and the first output terminal.