Bank of Ireland is closing 88 branches in the Republic, and 15 in Northern Ireland.
The branches, due to close by the end of September, are mainly self-service which don't have a counter service.
It says they all have a post office within 500 metres on average.
The bank is entering into a new partnership with An Post to offer banking services at over 900 locations, with longer opening hours.
The bank says it will continue to operate an extensive branch network with a strong nationwide presence of 169 locations.
