Mesenchymal stem cells (MSCs) are in the center of attention of many investigators due to easy isolation from many tissues. MSC capability to differentiate into many cell types makes them a starting point of many new therapies, especially in tissue engineering. However, understanding the process of MSC aging is crucial for selecting donors for cellular therapies, which is necessary for successful treatment. Cell changes can be divided into three major groups. Changes which affect their proliferate rate, differentiation capability and genome stability lead to decrease of their usefulness in new therapies. There are many tools that can be used to describe and measure some features of aging in MSCs but the essence of this process is still unclear. The aim of this review is to take a deep look into the influence of donor age and in vitro aging on MSC properties.