A circuit testing apparatus for testing capacitance of a capacitor of a device under test is provided. The circuit testing apparatus includes a measuring module, a first converting module, a processing module and a second converting module. The measuring module provides a testing signal, and determines the capacitance of the capacitor according to a signal measuring result of the testing signal. The first converting module is coupled to the measuring module for converting the testing signal to generate a testing input signal. The processing module is coupled to the first converting module and the device under test for transmitting the testing input signal to the capacitor, and amplifies an output signal generated by the capacitor to generate an amplified signal. The second converting module is coupled to the processing module and the measuring module for converting the amplified signal to generate the signal measuring result.