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Abstract: The martensitic transformation behavior, second phases and hardness of Ti51Ni49−x Si x shape memory alloys (SMAs) with x =0, 1 and 2at.% are investigated. The transformation temperature of one stage martensitic reaction B2↔B19′ is associated with the forward (M s) and reverse (A s) martensitic transformations, respectively. All experimental DSC results such as martensitic transformation peaks (M*) and reverse martensitic transformation peaks (A*) are increased and became sharper with increasing Si-content. The microstructure investigation of the studied SMAs (Ti51Ni49−x Si x ) showed that there are two types of precipitated second phase particles. The first one is Ti2Ni which mainly located at grain boundaries and intermetallic compound of Ti2(Ni+Si) phase distributed inside the matrix. The volume fraction of these two phases is increased with Si content. Additionally, a small amount of Si remained in solid solution of the matrix of Ti51Ni49−x Si x SMAs. Moreover, hardness of Ti51Ni49−x Si x SMAs is increased as the Si-content increases. [Copyright &y& Elsevier]