The aim of this pilot study was to assess whether a single mesenchymal stem cell intra-articular injection in the osteoarthritic joint gives a therapeutic effect. This trial study was made in order to better manage and structure further study on more dogs. Single injections of 3 million mesenchymal stem cell intra-articular injections were made bilaterally in the osteoarthritic elbow joints. The dog was examined before and after monthly stem cell therapy using stance analyser scales to determine the static weight of each limb. Weight balance between forelegs improved, but not significantly (p>0.05). A radiographic examination was made for both elbow joints before stem cell therapy and the second and fifth month thereafter. Calculations of sub-trochlear sclerosis in percentage were made using mediolateral projections. Sub-trochlear sclerosis in percentage significantly decreased (p<0.05) after stem cell therapy in both legs.