The electrochemical behaviour of Cu24Zn5Al alloy in a sodium tetraborate solution in the presence of 1-phenyl-5-mercaptotetrazole (PMT) has been investigated. Investigations have been carried out on the influence of PMT concentration, chloride ion concentration and the immersion time on the alloy behaviour by employing the technique of mass loss determination and by anodic polarization. Corrosion potential has also been measured and the surfaces of the alloy are recorded using optical microscopy. According to the obtained results 1-phenyl-5-mercaptotertazole shows good inhibiting properties for the investigated alloy. The inhibition mechanism is based on the formation of a Cu-PMT polymer film. Using the Langmuir isotherm the adsorption energy has been found to be in the interval from -33.8 to -37.7 kJ/mol.