More than 1,000 people attended a special mass at Knock shrine in Co Mayo.
Prayers were also said at Masses in a number of other counties, including a service at the Augustinian Church in Drogheda, Co Louth.
The day of remembrance was first initiated by the UK charity Road Peace.
It has been held every year on the third Sunday of November since it was adopted by the UN in 2005.
The Road Safety Authority said it was important to remember those who have been killed on Irish roads and their families.
The RSA said more than 22,600 people have been killed on Irish roads since the recording of road deaths began in 1959.
RSA Chairman Gay Byrne said today should serve as a reminder of just how vulnerable people are on the roads.
Mr Byrne said: 'To those who have not yet changed their behaviour and taken responsibility for their actions on the roads, I make a personal plea to you to reflect on the risks you take and the risk you force on others.'
Minister for Transport Noel Dempsey said today was 'a poignant reminder to us all just how devastating a road traffic collision can be'.
