The total reserves had risen by $21 million to $280.19 billion in the previous reporting week.
Foreign currency assets, a major component of forex reserves, were down by $999 million to $251.14 billion for the week ended July 19, the apex bank noted.
Foreign currency assets expressed in US dollar terms include the effect of appreciation or depreciation of the non-US currencies, such as the euro, pound and yen, held in the reserves, the apex bank said.
The apex bank said the gold reserves were unchanged at $21.55 billion during the week.
For the week under review, the special drawing rights (SDRs) were up by $9.5 million to $4.343 billion, while the country's reserve position with the IMF was also up by $4.8 million to $2.167 billion, RBI data showed.