Induced osteogenesis of mesenchymal stem cells (MSCs) may provide an important tool for bone injuries treatment. Human umbilical cord and adipose tissue are routinely discarded as clinical waste and may be used as noncontroversial MSCs sources. It still remains to be verified which source of MSCs is the most suitable for bone regeneration. The aim of this research was to investigate the osteogenic potential of human MSCs derived from adipose tissue (AT-MSCs) and Wharton's jelly of the human umbilical cord (WJ-MSCs) differentiated under the same conditions. Osteogenic differentiation of MSCs was detected and quantified by alizarin red S (ARS) staining for calcium deposition and alkaline phosphatase (ALP) activity, osteoprotegerin (OPG), and osteocalcin (OC) secretion measurements. Under osteogenic conditions, after 21 days of differentiation, the measured ALP activity and calcium deposition were significantly higher in the AT-MSCs than in the WJ-MSCs, while the OPG and OC secretion were higher in the WJ-MSCs vs. AT-MSCs. Low concentrations of OPG and high levels of OC in AT-MSCs and WJ-MSCs, prove that these cells reached an advanced stage of the osteogenic differentiation. The levels of OC secreted by AT-MSCs were lower than by WJ-MSCs. Both cell types, AT-MSCs and WJ-MSCs possess a potential to differentiate towards the osteogenic lineage. The observed differences in the levels of osteogenic markers suggest that after 21-days of osteogenic differentiation, the AT-MSCs might have reached a more advanced stage of differentiation than WJ-MSCs.