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Deformation mechanisms governing the cyclic stress-strain behaviour of a TiNi shape memory alloy are investigated in this work. In order to understand the implementation of these mechanisms during cyclic loading, three low cycle fatigue tests were performed and stopped at different stages. The first test was stopped after the first cycle, the second one after 40 cycles corresponding to the beginning of the stabilization of the cyclic strain-stress behaviour and the last one was carried out up to failure (3324 cycles). Submitted to fatigue loading, the response of the TiNi shape memory alloy presents a classical pseudoelastic response. Two deformation mechanisms, identified by TEM observations, are highlighted, the first one by twins and the second by dislocation slip and their interaction with precipitates. These two mechanisms evolve without competition during cyclic loading. In the same time, nanomechanical properties were also examined and an evolution of the microhardness or indentation modulus has been noticed.