Mesenchymal stromal cells (MSC) represent an interesting cell source for cell therapy, nevertheless their use in clinic involve an expansion step which could affect their quality because of replicative aging. Moreover, the proliferation rate depends on the MSC source. This work compares the proliferation kinetics at early and late passage of young and old Bone Marrow MSC (BM-MSC) and Wharton’s Jelly MSC (WJ-MSC) to know if senescence could affect their proliferation properties. Phenotype, cell cycle analysis, relative size and cell structure determination were performed by flow cytometry. Senescence was estimated by β-Galactosidase activity. Immunofluorescent staining was performed for proliferation antigen Ki67, protection enzyme against oxidative stress superoxide dismutase 2 (SOD2) and cytoskeleton. Results showed better proliferation properties for WJ-MSC compared to young and old BM-MSC. For WJ-MSC the high proliferation rate was linked to a lower senescent cells percentage and SOD2 expression. On the contrary, old BM-MSC have a low proliferation rate linked to an increase in G0/G1 cell cycle phase, an increase in cell size, a higher senescent cells percentage and SOD2 expression. The comprehension of the process of MSC proliferation and the development of strategies to prevent senescence could help to improve therapeutic efficacy.