Here we report a systematic theoretical study of the structure and electronic properties of Sn_n−1Pb and Pb_n−1Sn (n = 2−13) clusters and compare these results with pure Sn_n and Pb_n to understand the influence of the dopant elements. The calculations were carried out using the density functional theory with generalized gradient approximation for the exchange-correlation potential. Extensive search based on large number of initial configurations has been carried out to locate the stable isomers of Sn_n−1Pb and Pb_n−1Sn (n = 2−13) clusters. The relative stability of Sn_n−1Pb and Pb_n−1Sn (n = 2−13) clusters is analyzed based on the calculated binding energies and second difference in energy. The stability analysis of these clusters suggests that, while the substitution of Sn by Pb lowers the stability of Sn_n clusters, presence of Sn enhances the stability of the Pb_n clusters. The results suggest that while for Sn_n−1Pb, n = 4, 7, 10, 12 clusters are more stable than their respective neighbors, Pb_n−1Sn clusters with n = 4, 7 and 9 are found to be more stable. Based on the fragmentation pattern it is seen that for Sn_n−1Pb and Pb_n−1Sn clusters favor monomer evaporation of the Pb atom up to n = 11 and n = 12, respectively. Unlike this trend, the Sn₁₁Pb undergoes fission type fragment into Sn₅Pb and Sn₆ clusters. A comparison between our theoretical results and surface induced dissociation experiment shows good agreement, which gives confidence on the prediction of the ground state geometries.