Statistics Canada says manufacturing sales fell 1.3 per cent to $56.4 billion in December as sales of petroleum and coal products fell.
The agency says the drop for the final month of 2018 was the third consecutive month to see a decline.
Economists had expected an increase of 0.2 per cent, according to Thomson Reuters Eikon.
Statistics Canada says sales were down in 12 of 21 industries tracked, representing 72.7 per cent of manufacturing sales.
Sales in the petroleum and coal product industry fell 10.4 per cent to $5.2 billion, with a decrease in volume accounting for about half the decline.
In volume terms, overall manufacturing sales were down 1.2 per cent in December.
The Canadian Press