The inhibition effect of 1,5-dibenzyl-1H-pyrazolo[3 ,4-d]pyrimidine-4(5H)-thione‘‘MF1’’was estimated on the corrosion of mild steel in 1.0 M HCl solution using weight loss, Electrochemical Impedance Spectroscop y (EIS), Tafel polarization curves and theoretical calculati on methods. The results of the polarization curves show that the corrosion current density decreases 577.9 μ A/cm 2 to 38.5 μ A/cm 2 after addition of the inhibitor. The charge transfe r resistance increases 21.08 ohm.cm 2 to 402.2 ohm.cm 2 in the electrochemical impedance spectrum after ad dition of oil of the inhibotor.Potentiodynamic polarization c urves show that 1,5-dibenzyl-1H-pyrazolo[3,4-d]pyri midine- 4(5H)-thione act as mixed type inhibitor. The adsor ption of inhibitors obeys the Langmuir adsorption i sotherm, and the thermodynamic parameters (E a , K ads , ∆ G 0 ads) were calculated and discussed. Quantum chemica l calculations showed that the inhibitor has the tendency to be pr otonated in the acid and the results agree with exp erimental observations.