This work intends to evaluate the effects of wetting and drying cycles on soil shear strength. It is a study of great importance, specially for brazilian soils, since they are found in a tropical area, where there are periods well defined of raining and dryness.It is well known that long raining periods can saturate the soil, as well as during dryness it can occur a bigger evaporation than infiltration of water, what brings soil to an unsaturated state. Unsaturated soils have an additional strength component: the apparent cohesion. In nature, raining and dryness do not occur uniformly, because of that, the soil suction can reach different values, depending on its wetting and drying, thus being, wetting and drying cycles and the corresponding suction levels can affect the mechanical behaviour of soil.Aiming at verify the influence of such cycles of wetting and drying, soil shear strength was obtained through laboratory tests of direct shear with controlled suction, using PUC-Rio s developed equipment. Soil wetting and drying had been simulated in laboratory, reducing and increasing suction. Mature soil brought from the experimental field II of PUC-Rio, sifted and compact in laboratory, was used.Many series of laboratory tests had been carried out, modifying procedures related to applied suction levels. From the gotten results the influence, of wetting and drying cycles and reached levels of suction, was verified. Such influence also occurred, on total and water volume changes, during the shear.