Manufacturing sales fell 0.8 per cent in October to $48.7-billion after three straight monthly increases.
Despite the decline, Statistics Canada reports October's sales were the second highest of any month in 2011, surpassed only by September.
The agency blames the drop mainly on lower sales in the petroleum- and coal-product industries, as well as aerospace products and parts.
Statscan says the declines were partially offset by advances in vehicle parts, computer and electronic products, and wood products.
Constant-dollar manufacturing sales were down 0.9 per cent, their first decline after three months of advances.
Lower sales were reported in 13 of 21 industries, representing about two-thirds of Canadian manufacturing.
The reduction in sales largely came from non-durable goods manufacturers, whose sales fell 1.8 per cent in October, while durable goods sales rose 0.2 per cent.
Sales of petroleum and coal products fell 4.3 per cent to $7.3-billion — still the industry's second-strongest in 2011.
Aerospace product and part manufacturers reported a 9.7 per cent drop in production to $1.3-billion in October. Sales declines also occurred in food (down 1.1 per cent) and paper (down 3.6).
Vehicle parts were up 6.2 per cent, computer and electronic products rose 6.3 and the wood products increased 5.2.
Seven provinces posted lower manufacturing sales in October, with the largest dollar decreases coming in Alberta, New Brunswick and British Columbia.