Statistics Canada says manufacturing sales declined 0.9 per cent to $49.6-billion in January, the second decrease in seven months.
The agency blames the decline on a one-third drop in the aerospace product and parts industry as well as lower sales in the primary metals, machinery and other transportation equipment industries.
Excluding aerospace, sales were virtually unchanged from December.
Sales decreased in 11 of 21 industries representing approximately 44 per cent of manufacturing.
Sales of durable goods fell 2.4 per cent while sales of non-durable goods rose 0.6 per cent.
In constant dollar terms, manufacturing sales fell 1.1 per cent in January, the first drop in three months.
Production in the aerospace product and parts industry fell 34.0 per cent to $913-million in January, the third decrease in four months.
Manufacturing sales in the primary metal industry slipped 3.5 per cent to $4.1-billion.
In January, machinery manufacturers reported a 4.5-per-cent decline in sales to $3-billion, a second consecutive monthly decline.
Higher sales in the motor vehicle and parts industries offset a portion of the overall decline in manufacturing in January.
Sales in the auto assembly industry rose 2.6 per cent to $4.5-billion, the seventh consecutive month of increases. January sales hit the highest level since November 2007.
Sales in the industry have grown 37.4 per since June 2011, the most recent low.
Overall manufacturing sales declined in five provinces in January, with Quebec posting the largest decrease in dollar terms.