A new Enterprise Ireland survey finds one third have seen their sales fall this year, while the majority expect Brexit to add up to 10 per cent to their cost base.
Eight in ten exporters are either confident or very confident about international trading in 2021.
Julie Sinnamon, CEO of Enterprise Ireland says they have mixed views.
"What I would say is it is a tale of two halves. We have a group of companies which have continued to grow strongly, like digital technology etc.
"It's 89 days until January 1st, 2021 and what I would be saying to companies is that you have to be prepared. You have to have a no regrets policy," said Ms Sinnamon.
"One of the factors coming through in our survey is that 75 per cent of companies are saying logistics over customs are the biggest issue.
"There are supports in terms of custom grants to take on personnel to deal with the increased bureaucracy and customs declarations," Ms Sinnamon added.