"They have been engaged in acts of espionage and maintained dealings with terrorist organizations," the Indian foreign ministry said in a statement.
India will cut staff in its own embassy in Islamabad by the same amount, the statement added.
A spokesman at Pakistan's embassy in New Delhi did not immediately respond to a request for comment.
India expelled two Pakistani diplomats on May 31 after they were held for alleged spying, claims Islamabad said were "baseless."
Relations between the nuclear-armed rivals are strained and tit-for-tat expulsions of diplomats, often on charges of espionage, are common.
Neither country has a permanent ambassador in place and in the last month, each has accused the other of the illegal detention and torture of diplomats.