Statistics Canada says manufacturing sales fell 0.4% to $78.7 billion in July.
The agency says the move lower, which followed five consecutive monthly increases, came as sales fell in eight of the 21 subsectors it tracks.
Sales of chemical products fell 6.6% to $5.9 billion in July, as sales of resin, synthetic rubber, and artificial and synthetic fibres and filaments dropped.
Food manufacturing sales fell 1.4% to $13.9 billion on lower sales in the grain and oilseed milling industry group.
The petroleum and coal products subsector saw a 1.9% increase in sales to $10.4 billion in July, boosted by higher prices.
In constant dollars, total manufacturing sales fell 1.4% in July.