The purpose of the present study was to investigate the influence on structural improvement of the "terra-roxa" soil by means of application of barnyard manure, lime and mineral fertilizers. An experiment had been run by the Cereals Section from 1953, at the Central Experiment Station in Campinas, on 27 plots of corn, of terra-roxa soil of the "Chapadão" series. Analyses of soil samples from these 27 plots were made and samples were taken from these cultivated corn plots as well as from plots non cultivated for several years; they were passed through a 7.0 mm sieve and the aggregates separated into the following classes as to their diameters: 7.0 to 4.0mm, 4.0 to 2.0mm, 2.0 to 1.0mm, 1.0 to 0.5 mm, 0.5 to 0.25 mm and less than 0.25 mm. Comparing the results regarding the aggregates of the cultivated plots and non cultivated as well, it was found that in the former a decrease of the mean diameter of the aggregates occurred, same ranging from 1.25 mm to 0.5 or 0.79 mm. There is conclusive evidence of the decrease of their mean diameter, the main factor for this being the intensive tillage of the soil. Further, a correlation between the carbon content and the mean diameter of the aggregates was noted. Application of barnyard manure had as a result the increase of their mean diameter. No correlation was observed between the aggregation and the corn yield. The "terra-roxa" highly structured supports intensive work of the soil with no unfavorable effect on the corn plant development.