The country's Purchasing Managers Index (PMI) fell to a lower-than-expected 50.8, from 51.1 in the previous month. Any score above 50 represents growth.
Analysts had forecast a small rise in the pace of growth.
Recently released figures showed the wider Chinese economy growing at its slowest pace for more than five years.
Growth between July and September was 7.3% compared with a year earlier, down from 7.5% in the previous quarter.
"There remains downward pressure on the economy, and monetary policy will remain easy," said analysts at China International Capital after the PMI data was published on Saturday.
Beijing recently unveiled measures designed to stimulate consumer spending, including relaxing limits on home purchases and injecting billions of dollars into the country's biggest banks.
China's central bank has also cut certain inter-bank interest rates.
The government aims to achieve 7.5% economic growth this year, although many analysts believe it will struggle to meet this target. There is speculation it may take further steps to boost growth.
Such high levels of growth are needed to ensure enough jobs are created for China's huge and increasingly-educated population.
But the growth ambitions are much higher than expected rates in more developed economies - latest figures show the US economy growing at an annual rate of 3.5%.
Growth in China's manufacturing sector slowed in October, an official survey suggests, reinforcing concerns about a slowdown in the wider economy.