During the reporting month, it bought USD 4.893 billion and sold USD 1.940 billion in the spot market, according to the latest data from the central bank.
In June, the central bank was also net purchaser at USD 3.291 billion after it bought USD 4.971 billion while it sold USD 1.680 billion.
The RBI intervenes in the foreign exchange market to contain volatility in the rupee market.
Last year in July, RBI had net bought USD 1.4 billion of dollar. In FY17, it net purchased USD 12.351 billion of the US currency as it bought USD 71.764 billion and sold USD 59.413 billion in the spot market.
In the forward dollar market, the outstanding net purchase at the end of July was USD 26.450 billion, RBI data showed, while the net forward purchase at June-end was USD 17.081 billion.