The 2-propargyl-5-o-hydroxyphenyltetrazole (PHPT) has been tested as corrosion inhibitor for low carbon steel in simulated cooling water. The polarization curves showed that PHPT acts as mixed-type inhibitor. Its inhibition efficiency was found to enhance with increase of the inhibitor concentration and immersion time due to the formation of the inhibitor film on the metal surface as indicated by electrochemical impedance spectroscopy measurements. To complete the formulation further, a non oxidizing biocide was added. Its presence with PHPT does not affect its inhibitory performance and it can be served as a basic component of the formulation for cooling water system.