The decline was on account of a substantial fall in foreign currency assets (FCAs), a major component of the overall reserves.
In the previous week ended September 30, the reserves had surged USD 1.223 billion to reach a life-time high of USD 371.99 billion.
In the reporting week, foreign currency reserves dipped by USD 4.316 billion to USD 342.394 billion.
FCAs, expressed in US dollar terms, include the effect of appreciation/depreciation of non-US currencies such as the euro, pound and the yen held in the reserves.
The special drawing rights with the International Monetary Fund declined by USD 10.4 million to USD 1.476 billion, while India's reserve position with the Fund dipped by USD 16.5 million to USD 2.369 billion, the apex bank said.