High temperature corrosion tests were done for 1.25Cr-0.5Mo steel and 347H and 31OS stainless steels in simulated syngases of various compositions at atmospheric and high pressures. For 1.25Cr-1Mo steel, the weight gain increases linearly for 100h and is accelerated by total gas pressure. For stainless steels, the weight gain is accelerated with increase of H2S content and suppressed with increase of H2O content of the simulated syngas. The corrosion of 31 OS stainless steel is one-half to one-third that of 347H stainless steel.