Sales of commercial housing rose 28.7 percent year on year to hit 514.33 million square meters, down 8.4 percentage points from the first quarter.
NBS figures released on Monday also showed China's gross domestic product growth slowed to 7.6 percent in the first half, down from 7.7 percent in the first quarter.
Experts attributed the deceleration of fixed-asset investment to sluggish exports, a liquidity crunch, and the transformation and upgrading of Chinese enterprises.
"Investment-driven growth can no longer be translated into the sustainable development of the Chinese economy. Instead, consumption-led economic restructuring is the government's priority," said Ma Yao, a macro-economy researcher with China Investment Consulting Corp.
Chinese Premier Li Keqiang said last week that China is in a phase in which it must rely on economic transformation and upgrading to maintain continuous and healthy development.
He said China must quicken its reform in the areas of administration, taxation, finance and pricing with the aim to let the market mechanism play a better role, make private investment more active and the market more vigorous.
More support will be channeled to the central and western part of the country, especially poverty-stricken areas, Li said, adding that the more affluent eastern part of China should strive for development at a higher level through economic transformation and upgrading.
NBS figures released on Monday also showed China's gross domestic product growth slowed to 7.6 percent in the first half, down from 7.7 percent in the first quarter.