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The Shanghai Composite Index, which covers both A and B shares, was down 11.22 points at 3,039.31.
The Shanghai A-share index fell 0.37 percent, or 11.77 points, to 3,182.54, while the Shenzhen A-share index shed 0.36 percent, or 4.89 points, to 1,335.94.
China's central bank announced Sunday it would raise the amount of money that lenders must keep in reserve by 0.50 percentage points.
It was the fourth such move this year as the government continues a campaign to curb fast-pace lending blamed in part for high inflation.