Rock masses are submitted to biaxial and triaxial states of stress. Deformability and strength properties of rocks under such conditions are essential data for calculating bearing capacity of foundations, design of dams, mining excavations, oil exploration, tunnelling etc. For these purposes, laboratory and in situ tests are of great importance. Studying rock behaviour when submitted to triaxial loading is of great concern, due to the difficulty in carrying out biaxial tests and because triaxial state of stress is more common. This thesis presents the design and construction of a triaxial cell for laboratory tests in rocks, which is able to support a confining pressure as high as 70 MPa. The equipment allows internal specimen instrumentation. Top and bottom pore-pressure measurements have been predicted, and fluid percolation through the specimen is possible. Tests on steel and rock specimens were carried out to comission the equipment. The rock tested is a leptinite gneiss found in the city of Rio de Janeiro (Morro Dona Marta).