Preliminary figures from the Central Statistics Office show that seasonally adjusted exports fell by 1% to €9.168 billion in May compared to April.
Seasonally adjusted imports rose by 7% to €5.206 billion during the same time, the CSO added.
This lead to a 10% fall in the seasonally adjusted trade surplus to €3.962 billion in May from €4.404 billion in April.
The CSO said that exports of organic chemicals rose by 19% to €2.025 billion on an annual basis in May, while exports of electrical machinery, apparatus and appliances soared 127% to €477m. But exports of food and live animals fell by 8% to €781m.
Today's figures also show that imports of road vehicles rose by 48% to €381m in May compared to the same time last year, while imports of mineral fuels and related materials fell by 19% to €353m.
On a geographical basis, the EU accounted for 52% of the country's total goods exports in May, with the biggest markets in Belgium and the UK.
The US was the main non-EU destination, accounting for 29% of total exports in May.
Meanwhile, the EU accounted for 62% of the value of imports in May, with 24% of total imports coming from the UK. The US and China were the main non-EU sources of imports, the CSO added.
Commenting on today's figures, Merrion economist Alan McQuaid said there was very strong growth in Irish merchandise exports in 2015 and another solid performance is expected for 2016.
But the economist cautioned that in a "post Brexit world" it is hard to tell how things will play out.
He said that one can only speculate as to how Brexit will impact Ireland in the coming months and years, but there is likely to be a negative impact on trade.
Mr McQuaid pointed out that the UK is the second largest single-country for Ireland's goods and the largest for its services. At the same time, Ireland imports 30% of its goods from the UK.
"While the UK might only account for 16-17% of Ireland's total exports, 30% of all employment is in sectors which are heavily related to UK exports. SMEs (particularly agri-food and tourism) will likely be more affected than larger companies by the introduction of tariffs and barriers to trade," he added.