Salinization of soil has a negative impact on the activity of microorganisms and thus leads to disturbances in the cycling of nutrients in the soil environment. Our goal was to determine what amount of salt has some measurable negative effect on enzymatic activity of soils, namely on native proteases. Inhibition of proteases was detected at as little as 0.5 mg of chloride salts in an organomineral horizon from an oak stand, but in most cases, some inhibitory effect appeared from 1-2 mg of salt added to the soil. Although the stimulatory effects of salt were also observed, in those cases it probably was not associated with activity of the microbial community. Our results indicate the levels from which the activity of microorganisms will probably decrease and organic matter decomposition will be slowed.