Tourists from the Republic pumped £67m into the economy last year as the total number of holiday makers from across the border rose by 39%.
And the number of Northern Ireland residents choosing to holiday at home also increased, by 13%, while the total number of trips taken resulted in £190m being spent in the local economy.
The Northern Ireland Tourist Board (NITB) released the figures as it unveiled a new £1m marketing campaign for 2010 on the theme of Relax, Rejuvenate and Refresh.
The Tourist Board said its most recent campaign, Explore More, launched in autumn, generated a return on investment of £23 for every £1 spent.
NITB chief executive Alan Clarke says they made the most of the economic situation by offering visitors compelling reasons to stay in Northern Ireland.
“The economic climate and strong euro has definitely contributed to an increase in visitor numbers domestically and from the Republic of Ireland.
“Against this backdrop, it has been crucial that our campaigns highlight the world class attractions, hidden gems and unique stories that we have to offer here, giving people more reasons to visit and, equally important, to come back,” said Mr Clarke.
“Last year’s autumn campaign in Northern Ireland and the Republic of Ireland generated a return on investment of £23 for every £1 spent and we are hopeful that this year’s campaign can improve on that.