A characteristic effect of inorganic neutral salts on myrosinase was discovered. The salts containing monovalent anions had a remarkable inhibitory effect on the ascorbate-activated enzyme, but little on the non-activated enzyme. Such an effect was elucidated to be due to the anion. For the ascorbate-activated enzyme, a linear relation was obtained by plotting the logarithms of the enzymatic activity against the square roots of the ionic strength of the salts. Therefore, the effect of monovalent anions is ascribable to the ionic strength of the solvent. The Km values of the activated and non-activated enzyme were increased by the presence of the monovalent anion.