The inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1,2,4-trizole-3-thiol (APTT) in 2.5M H2SO4 solution and the effect of hydrodynamic condition on inhibition process were studied.The hydrodynamic condition experiments are simulated by rotating cylinder electrode (RCE).Change of open circuit potential (OCP) with immersion time,potentiodynamic polarization,and electrochemical impedance spectroscopy (EIS) were used to study the effect of hydrodynamic condition on the inhibition process.Results obtained from changes of open circuit potential (OCP) with immersion time,potentiodynamic polarization,and impedance measurements are in good agreement and indicated that the inhibition process was flow rate dependence.