The medal has been named after the former UN Secretary General and Nobel Peace Prize winner, Dag Hammarskjold, who was killed in a 1961 plane crash while on a peace mission to Congo.
After the ceremony, the Minister for Defence said Irish troops might soon be returning to the Congo.
The dangers of peacekeeping were dramatically brought home to people here when 17 Irish soldiers were killed in the Congo just over 40 years ago. It was the army's first major foreign assignment and the brutal deaths shocked the country.
Since then 83 Irish soldiers have died while serving with the UN - mostly in the Lebanon. Some were killed on duty, others died in accidents.
Soldiers killed in action have already been awarded the military star.
But now all troops who died while serving have been given the new posthumous award.
This afternoon in Dublin, families of the Irish dead were given the awards at Cathal Brugha Barracks.
United Nations medals were also presented to 37 members of the Defence Forces who worked in Rwanda after the genocide there nine years ago. They carried out administrative, engineering and logistical work, and helped to bury the dead.
Afterwards, the Minister for Defence Michael Smith said about 40 members of the army ranger wing might soon be off to serve in the Congo, if requested by the United Nations.
