Analyses of soil samples from different cropping systems were made to define the structural state of a red-yellow podzolic soil at the Experimental Station of "Monte Alegre do Sul". Soils from the following plots under different cropping systems were studied: a. - corn crops during 15 years, b. - fruit crops and c. - forest with Eucalyptus. Mechanical analyses and determinations of pH, total N and C, and exchangeable Ca, Mg and K were made. The aggregate distribution was run by dry sieving and the stability was made by wet sieving. The results showed a decrease of the mean geometric diameter of the aggregates from the forest plot (2.55 mm) to the fruit plot (2.35 mm) and to the corn plot (2.25 mm). The decrease of the water stability of the aggreagates on the yearly cultivated plot was remarkable: 87% of the aggregate from the forest plot " were water stable, while the aggregates from the corn plots only were 31% stable. The reason of this behavior of the soil is discussed.