Statistics Canada says wholesale sales fell 0.5 per cent to $63.2 billion in September, led lower by the machinery, equipment and supplies and the personal and household goods subsectors.
Economists had expected an increase of 0.3 per cent for the month, according to Thomson Reuters Eikon.
Sales were down in five of the seven subsectors tracked.
The machinery, equipment and supplies subsector fell 2.0 per cent to $13.0 billion in September, while the personal and household goods subsector dropped 1.6 per cent to $9.0 billion.
The building material and supplies subsector increased 1.5 per cent to $9.5 billion.
In volume terms, Statistics Canada says wholesale sales fell 0.7 per cent.