An experimental investigation was conducted on undisturbed sensitive Leda clay samples from the Ottawa area using a simple shear device. Both small strain and large strain tests were conducted under a range of consolidation stress levels. The Carleton University simple shear device was improved to measure shear properties at small strain amplitudes.Strength tests at large strain levels were performed in order to study the monotonic and cyclic behaviour of sensitive Leda clays, while quasi-cyclic tests were carried out to obtain material specific modulus and damping curves at small strain amplitudes.Strength tests indicate that Leda clay might reach a steady state during monotonic loading. Under cyclic loading, the clay deformed with progressively increasing cyclic strain, and liquefaction becomes a concern when cyclic stress amplitudes exceed at least 60% of their monotonic undrained shear strength. Few small amplitude stress or strain cycles do not produce significant strength loss or do not change the subsequent shear behaviour.Successful application of small strain quasi cyclic tests proved to be an optimum means of obtaining modulus reduction and damping data in the laboratory. Material specific modulus reduction and damping ratio curves are presented for Ottawa area Leda clay based on this experimental data. These results show that the behaviour of sensitive clays cannot be simply equated to that of typical non sensitive clays with high plasticity index, if accurate site response analysis results are required.ii