Well over half (58%) of Irish SMEs believe Brexit will have a negative impact on their future business, with seven in ten of them predicting an adverse effect on the wider economy.
Despite this, the latest Brexit Sentiment Index from AIB reports just six percent of businesses here have a Brexit plan in place.
This figure drops to 5% for companies in Northern Ireland.
In the Republic, businesses in the food and drink sectors are most likely to have a plan in place (11%), followed by tourism (9%) and transport (7%).
The research also found the manufacturing, retail and tourism sectors are the most negative about the impact of Brexit on Ireland.
According to the index, chief among all concerns is the impact of potential new trade tariffs, while larger businesses more likely to have Brexit plan in place.
Head of Business Banking with AIB Catherine Moroney said the research indicates that larger businesses are more likely to have a formal Brexit plan and that "it's critical to plan for the worst now.
"When businesses do seek financing, one of the key questions we in AIB ask them about is their business' Brexit readiness and the potential impact Brexit may have on their business in a harder line Brexit scenario."
The AIB Brexit Sentiment Index research in Q4 2017 showed that one in five Irish exporters were considering new markets.
