Pešter peat belongs to the type of acid peats. Its pH value in n KCl is between 4.6 and 4.9. As such, it cannot be directly applied in the production of the compost for agaricus mushrooms, because these mushrooms require the alkaline pH value, i.e. pH value in n KCl greater than 7.3. To satisfy this condition, the peat was calcified, and the experiment was established in the mushroom growing plant, owned by Milan Božić, at Leštane. Peat calcification was performed with fine-ground CaCO3, chalk, hydrated lime, and zeolite in various ratios. The experiment was established in ten variants. The best results were obtained by the variants in which calcification was performed with 4% hydrated lime, and by variant with 2% hydrated lime + 2% chalk + 2% zeolite.