The present invention relates to a novel glycoprotein-A repetitions predominant protein (GARP) surface marker for mesenchymal stem cells, specifically activated mesenchymal stem cells, and to a method for the isolation and/or identification of mesenchymal stem cells based on the detection of the glycoprotein-A repetitions predominant protein (GARP) surface marker. The invention also relates to mesenchymal stem cells expressing said marker and to the uses thereof.