The results of gravimetric and potentiostatic studies of pyridinium salts, derived from alkenylphenols, as inhibitors of hydrogen sulfide corrosion of steel St 3 in aqueous saline and hydrocarbon systems and testing the salts for bactericidal activity against sulfate-reducing bacteria (SRB) are reported. It has been found that the test compounds with a concentration of 50-150 mg/L slow down the cathodic and anodic reactions and significantly increase the polarization resistance (R (p)) of St 3. The best protective properties have been shown by 1-(2-propenylphenoxytetramethylene)-N-pyridinium bromide (III) and 1-(2-allylphenoxytetramethylene)-N-pyridinium bromide (VI): the corrosion protection by III and VI is respectively 87 and 83% at a concentration of 50 mg/L or 96 and 93% at a concentration of 150 mg/L. The pyridinium salts synthesized in this study also exhibit bactericidal activity in a concentration of 50-200 mg/L. High bactericidal properties have been found for 1-(2-propenylphenoxytetramethylene)-N-pyridinium bromide. The SRB growth inhibition at its concentration of 50 or 75 mg/L is 75 or 100%, respectively.