An ESD clamp circuit applied to a power amplifier is provided. The ESD clamp circuit includes a first line, a second line, a first circuit, a second circuit, an ESD detecting unit, a buffer unit, and an ESD clamp unit. The first line is coupled to the output terminal of the power amplifier. The first circuit is coupled to the first line. The second circuit is coupled to the first circuit. The ESD detecting unit is coupled to the first circuit and the second line. The buffer unit is coupled to the second circuit, the second line and the ESD detecting unit. The ESD clamp unit is coupled to the buffer unit, the first line and the second line. Therefore, at normal operation mode, the problem of signal loss caused by the leakage current of ESD clamp circuit can be avoided.