An experiment was made in pots using a "Terra Roxa Estruturada" soil in order to study the effect of urea, sodium nitrate, ammonium sulfate and di-ammonium phosphate on the soil pH. The pH measure were made 15, 30, 45 and 60 days after begining the incubation period. The nitrogen was employed at the rate of 100 kg/ha. The main conclusions were as follows : 1 - Sodium nitrate did have any effect on the soil pH. 2 - Ammonium phosphate and ammonium sulfate made the soil pH decrease. 3 - Urea did not show any concludent result.