The August index was the highest in 16 months reflecting China's efforts to spur its slowing economy, the world's second-largest after the United States.
The August number was also the second straight monthly expansion, the China Federation of Logistics and Purchasing said. Any number over 50 on the index denotes expansion while any number below that denotes contraction.
Zhao Qinghe, a senior statistician with the National Bureau of Statistics, told the official Xinhua News Agency the new data showed the manufacturing sector has stronger growth impetus, and the economy is firming in a more evident way.
The August increase was credited to expansion of new orders, whose reading reached 52.4, up sharply from July's 50.6. New export orders rose to 50.2, up by 1.2 points.
There had been a number of signs showing the Chinese economy is slowing down, including the economic growth rate, which dropped to 7.5 percent in the second quarter from the first quarter's 7.7 percent.
Chinese policymakers are now concentrating on boosting domestic demand as external demand weakens.
"China's overall economic growth shows a positive situation, along with the accelerated implementation of fiscal plans," Liu Ligang, chief economist in China with ANZ Group, told China Daily.