The invention relates to an electrostatic discharge protecting circuit with ultra-low standby leakage current for twice supply voltage tolerance. The electrostatic discharge protecting circuit of the invention includes a substrate driver, a third transistor, a start-up circuit, a RC circuit and a second resistor. The substrate driver has a first transistor and a second transistor in serious connection. The start-up circuit has a fourth transistor and a fifth transistor with diode-connected. The RC circuit has a first resistor, a sixth transistor and a seventh transistor in serious connection. Compared with the prior art, the electrostatic discharge protecting circuit with ultra-low standby leakage current for twice supply voltage tolerance of the invention with advantages of low standby leakage current, high ESD robustness, and no gate-oxide reliability issue is an excellent circuit solution for on-chip ESD protection design for mixed-voltage I/O buffers in nanometer CMOS technologies.