The country's exports edged up 0.7% to $14.598 billion, while imports grew by 2.3% to $19.492 billion, the office said in a statement.
The export-import ratio fell to 74.9% from 76.1% in the first nine months of 2018.
In September alone, Serbia's exports went up 1.5% on the year to $1.648 billion and imports edged down 0.6% to $2.076 billion.
($ = 0.896355 euro)