The paper presents the impact of demographic ageing on the size and age composition of the labour force in Serbia. With an unchanged rate of activity, demographic ageing will lead to a reduction in the size of work force. After leaving the working age of baby-boom generations after 2010 a continuous decline of working age population is expected. Even expected immigration after 2020 in 90% cases will not prevent its further decline. Certain institutional measures, such as moving the age limit for leaving the labour force, can mitigate the negative effects of demographic trends. .