The business at these exchanges stood at Rs 45.53 lakh crore in the same period of last financial year, the regulator said in a statement.
Maximum fall in the turnover was seen in bullion followed by energy, metals and agricultural commodities.
According to the FMC data, the turnover from bullion fell by over 70 per cent to Rs 6,18,569 crore during April-July 15 of the 2014-15 fiscal, from Rs 20,95,113 crore in the year-ago period.
In turnover from agricultural commodities also fell by over 14 per cent to Rs 3,64,574 crore from Rs 4,22,890 crore in the same period.
The turnover of the commodity exchanges has been declining since the imposition of commodity transaction tax. The investors' confidence has also come down in the futures trading after the Rs 5,600 crore payment crisis at the National Spot Exchange Ltd (NSEL), analysts said.