In the reporting month, the central bank bought USD 3.788 billion, while it sold USD 2.529 billion in the spot market, according to the latest RBI data.
In August too, the central bank was net purchaser of 3.226 billion of the greenback, buying USD 4.556 billion and selling USD 1.330 billion in the spot market.
The RBI intervenes in the foreign market to contain volatility in the rupee and not set a price band.
Last year in September, the RBI had net purchased USD 4.649 billion and had sold USD 4.392 billion, while it bought USD 9.041 billion from the spot market.
In financial year 2016, the central bank was again a net buyer to the tune of USD 10.209 billion.
In the forward dollar market, the outstanding net purchase at the end of September was USD 31.131 billion, while the net forward purchase at the end of August was USD 32.823 billion, the data showed.