The aim of the study was evaluation of the influence of sewage sludge from dairy on the numbers of the ammonifying and nitrifying bacteria and on the nitrification and amonification rates. The field experiment was estabilished on brown soil. The experiment included the following treatments: 1 – soil + sewage sludge from dairy, 2 – soil + sewage sludge from dairy + farmyard manure (FYM), K – soil control, no sludge. Sewage sludge was applied at the rate 22 t ha-1 yr-1 and FYM at the rate 20 t ha-1 yr-1. It was found out that the effect of sewage sludge from dairy on the number of nitrifying bacteria was stimulated. Sewage sludge did not influence the number of ammonifying bacteria. Fertilization of sewage sludge increased amonification rates and inhibited the nitrification process.