A resistor-capacitor (RC) oscillator with shared circuit architecture includes a current mirror circuit, a comparator circuit, a bias voltage generator, and a clock buffer. The current mirror circuit utilizes a plurality of transistors to perform current control, to adjust a second current on a second current path according to a first current on a first current path. The comparator circuit includes a first transistor, a second transistor, a resistor, and a capacitor, wherein a comparison result signal generated by the comparator circuit corresponds to a voltage of the capacitor. The bias voltage generator generates a bias voltage as a comparator reference voltage between the first transistor and the resistor. The clock buffer buffers the comparison result signal to generate an output signal. The bias voltage generator at least shares the resistor with the comparator circuit, and the RC oscillator may achieve targets of low cost and high performance.