Just a few investigations have studied the function of various temperatures in distribution system mild steel corrosion. Generally, increasing temperatures caused the accelerated corrosion of mild steel. In addition, the average of chemical processes were increased as the temperatures were increased regarding to Arrhenius' Law. The synthesis and characterization of a novel organic corrosion inhibitor 4-(((5-ethyl-1,3,4-thiadiazol-2-yl) imino) methyl) phenol, for mild steel in hydrochloric acid was successfully reported for the first time. This inhibitor is tested as corrosion inhibitor on a mild steel sample MS in 1 M hydrochloric acid solution using Potentio-dynamics (PD) and Electrochemical Frequency Modulation (EFM) method. The results obtained indicate that inhibitor acts as an excellent corrosion inhibitor for mild steel sample in HCl solution with efficiency above 90%. Changes in the results parameters suggested adsorption on the surface of mild steel sample, which it leading to the formation of protective coating layer. However, this protective layer becomes weak when the temperature of the solution increases.