The trade deficit, which is for goods only, rose to 2.624 billion euros ($2.94 billion) in the period. In August alone, the gap widened 27 percent to 1.16 billion euros from the same month in 2015 as imports jumped almost 11 percent, while exports rose 6.1 percent.
In June-August, exports outside of the European Union slumped 14 percent and imports from non-EU countries fell 3.2 percent. Traditional Portuguese export markets outside Europe, such as Angola and Brazil, have seen sharp economic slowdowns recently.
But exports to European Union countries, Portugal's main market, rose by 4.6 percent while imports from those countries increased by 1.1 percent.
Helped by growing exports and domestic consumption, Portugal's economic growth accelerated to 1.5 percent last year from 0.9 percent in 2014, but analysts now expect a slowdown this year to around 1 percent growth partly due to weaker export growth.