Exports were down 20% last month, according to the latest figures from the Central Statistics Office.
The sector was weaker than expected, recording a seasonally adjusted trade surplus of €2.9bn, the lowest surplus since April 2011.
The driving factors behind the decrease were drops in exports of Chemicals and related products and increases in imports of transport equipment, including aircraft.
The flourishing export sector has long been seen as the driving force behind Ireland's economy.
The expiry of a number of patents is being blamed for the sharp drop in pharmaceutical products.
Commentators have said the one saving factor on the export side is the strong performance of the services sector, which has seen an annual increase of almost 10.5% in volume terms in the first half of the year.