In this present work one searched to evaluate the characteristics of shear strength and the suction-moisture relation of a tropical mature soil found in experimental field II of PUC-Rio, located in the city of Rio de Janeiro. For the determination of the shear strength of this soil, direct shear test in submerged samples using conventional equipment and direct shear tests with controlled suction in samples with natural moisture had been executed. The direct shear tests with controlled suction had been executed using the equipment developed in PUC-Rio for De Campos (1988), in which it uses the technique of translation of axles developed by Hilf (1956) for the control of the applied suction. Tests for the measurement of the suction which uses the filter paper method was carried through for the determination of the suction-moisture relation. Through the results of this test, the determination of the soil-water characteristic curve of this soil was possible. Diametrical compression test had also been carried through in order to establish a relation between the tensile strength of this soil versus its suction. Through the analysis of the experimental results, the determination of the shear strength envelope in tri-dimensions was possible considering the proposal of Fredlund et al. (1978), on which it bases on the use of the variables of tension (normal tension n - ua) and (ua - uw).