TiSnSb shows an excellent behavior as negative electrode for Li-ion batteries. However the role of Ti is still unclear in the mechanism. To better understand the role played by the transition metal on both the mechanism and the performance of TiSnSb, a progressive substitution of Ti by Nb has been achieved. A full study focuses on the electrochemical mechanisms of the Ti1−y Nb y SnSb system with 0 ≤ y ≤ 1 vs Li by combining in situ XRD and Mössbauer, and EXAFS analyses. The electrochemical mechanism is found to be a reversible conversion mechanism: MSnSb + 7Li ↔ Li3Sb + 1/2 Li7Sn2 + M0. The lithium is found to react simultaneously with both Sn and Sb. Nb-rich alloys have been found also to be very promising negative electrode demonstrating the versatility of the MSnSb electrode material family for Li-ion battery application. Using the appropriate electrode formulation, the good cycling life of TiSnSb is not affected by its substitution by Nb.