Disclosed is a true random number generator and a method for generating a true random number. The true random number generator includes a sampling circuit and a random number generating circuit. The sampling circuit is configured to sample N voltage(s) of N capacitors according to a clock signal and thereby generate N sample value(s), in which the N is a positive integer. The random number generating circuit is configured to generate a random number according to at least a part of the N sample value(s).