In this study, our investigations showed that the increasing concentrations of all examined mono alcohols caused a decrease in the V (m), k (cat) and k (cat)/K (m) values of Bacillus clausii GMBE 42 serine alkaline protease for casein hydrolysis. However, the K (m) value of the enzyme remained almost the same, which was an indicator of non-competitive inhibition. Whereas inhibition by methanol was partial non-competitive, inhibition by the rest of the alcohols tested was simple non-competitive. The inhibition constants (K (I)) were in the range of 1.32-3.10 M, and the order of the inhibitory effect was 1-propanol > 2-propanol > methanol > ethanol. The Delta G (not equal) and Delta G (not equal) (E -aEuro parts per thousand T) values of the enzyme increased at increasing concentrations of all alcohols examined, but the Delta G (not equal) (ES) value of the enzyme remained almost the same. The constant K (m) and Delta G (not equal) (ES) values in the presence and absence of mono alcohols indicated the existence of different binding sites for mono alcohols and casein on enzyme the molecule. The k (cat) of the enzyme decreased linearly by increasing log P and decreasing dielectric constant (D) values, but the Delta G (not equal) and Delta G (not equal) (E -aEuro parts per thousand T) values of the enzyme increased by increasing log P and decreasing D values of the reaction medium containing mono alcohols.