The index, a gauge of the understanding, views and projections of business people, has been declining all year. In the second quarter it was 5.8 points lower than the first quarter.
According to the NBS, Chinese entrepreneurs in all economic sectors were much less confident in the July-September period.
The property sector was the least confident. Its index plummeted to 96.4 points in the third quarter, a decrease of 22 points from that in the second quarter.
The confidence index of the manufacturing industry also fell notably in July-September to 119.3 points, down 13.6 points from the previous quarter.
On Thursday, the NBS said China's business climate index (BCI),a key gauge of corporate performance, dropped to 128.6 points in the third quarter, down 16.1 points from the same period last year. In the second quarter the index fell 8.8 points from 137.4 points.
It was the first time China's BCI fell below 130 points since the outbreak of the Severe Acute Respiratory Syndrome (SARS) epidemic in early 2003. The 100-point mark is seen as a definition between depression and prosperity.