This paper reports the results of two experiments earned out in Ribeirão Prêto experiment station to study the effects of two nitrogen fertilizers, Chilean nitrate and ammonium sulfate on corn yield. The levels of N used were 80 and 160 kg per hectare applied as side-dressing at 30, 60 and 80 days after the germination. The types and levels of N were compared in presence of PK that were applied in the furrow at planting time, respectively as superphosphate and potassium chloride, both in the amount of 80 kg per hectare. Two other treatments, no fertilizer and PK alone were included as controls. The results indicated that the application of PK increased the yield in 50% in relation to the check. No differences were found between types and levels of N. Both levels of N increased the yield in 33% when compared with that of the PK treatment.