The stand-alone profit for Jul-Sep 2009 quarter stood at Rs 3,852 crore versus Rs 4,116 crore in the same period a year ago accounting to the fall.
The tumble has been attributed to the fall in crude oil and refining margins.
RIL's total income jumped 5.88 per cent to Rs 47,476 crore during Q2 from Rs 44,839 crore in the corresponding quarter from the previous year.
The company's revenue from refining business grew nearly 9 per cent to Rs 39,564 crore, while income from petrochemical business plunged 14.20 per cent at Rs 13,340 crore.
Revenues from the oil and gas segment including exploration, development and production tripled to Rs 2,937 crore in the quarter, the company said in its filing with the Bombay Stock Exchange (BSE).
In a statement, RIL chairman, Mukesh Ambani spoke about the completion of the new SEZ refinery and the deep water, oil and gas K-G D6 block and their safe and stable ramp-up and termed them 'noteworthy accomplishments'.
"These projects have contributed meaningfully in RIL achieving a record level of profits despite the challenging business and economic environment," Ambani said.