The manufacturing purchasing managers' index (PMI), a gauge of factory conditions, stood at 51.6 in October, the National Bureau of Statistics (NBS) said, compared to 52.4 in September, which marked a five-year high.
Anything above 50 is considered growth while a figure below that number points to contraction. Analysts surveyed by Bloomberg News had expected a reading of 52.
October's week-long National Day holiday slowed down production and new orders growth, and energy and pollution- intensive industries shifted peak load or reduced production due to tightened environmental controls in some regions, NBS analyst Zhao Qinghe said in a statement.
But "the manufacturing sector continues to maintain an expanding momentum", he said.
The figure came after China registered slightly slower growth in the third quarter, with the economy expanding at 6.8 percent.
Analysts say it sets the ground for the government to tackle long-term economic issues such as soaring debt and property-led growth.