In the same period last year, RBI was a net purchaser of the greenback, as it had bought $16.301 billion.
In August, and July, it had sold $2.323 billion and $1.87 billion, respectively, on a net basis.
The apex bank said that In April, May and June, it had, on net basis, sold $2.483 billion, $5.767 billion and $6.184 billion of the US currency, respectively.
In September 2017, RBI had net bought $1.259 billion of dollar, after it purchased $3.788 billion and $2.529 billion in the spot market.
RBI maintains that its intervention in the foreign exchange market is to curb volatility in the rupee and not to target a level of the domestic currency.
The central bank has been very active in the past few months in the spot market to save the rupee which got battered against the US dollar.
The domestic currency fell to a historic low of Rs 74.1 against the dollar in October.
In FY18, the apex bank had net purchased $33.689 billion of US dollars from the spot market. It had bought $52.068 billion from the spot market, while selling $18.379 billion.
In FY17, RBI had bought $12.351 billion of the US dollars on a net basis.
In the forward dollar market, the outstanding net forward sales at the end of September was $1.358 billion, compared with a purchase of $5.730 billion in August, according to RBI data.