A comprehensive experimental investigation was performed on block samples of two sensitive clays taken from the sites of recent slides in Quebec. Both isotropically consolidated drained and undrained triaxial tests were carried out on specimens trimmed at various angles from the vertical direction. Direct and indirect drained tension tests were also performed so as to cover the entire stress range from tensile to compressive stresses beyond the preconsolidation pressure.Results of this study showed that the effective stress strength envelopes are pronouncedly nonlinear and strongly anisotropic in the working stress range usually encountered. The ratio of minimum strength to strength of vertical samples varies from 0.54 to 0.70. The drained tensile strength is also anisotropic, the value obtained for fracture across stratification is about three times that along stratification. The time to failure has an important effect on the peak strength.The post-peak behavior was studied and it is shown that the strength at large strains may be deduced from results of CIU and CID tests.The modulus of deformation varies with consolidation pressure in a manner similar to that of the peak strength envelope. It is essentially isotropic, but decreases with strain rate.Finally, application of these results to slope stability problems is discussed.