The US government denied that the diplomat had been involved in espionage, and the expulsion brought ties between the two countries to a new low.
Chavez identified the expelled attache as Commander John Correa.
"John Correa has to leave the country immediately," Chavez, a virulent critic of the United States, said in a speech at a Caracas theatre to mark the seventh anniversary of his coming to power.
"We have decided, in diplomatic terms, to declare him persona non grata, in plain Spanish that means to throw out of the country an officer at the US military mission for spying," Chavez said.
The socialist president, a virulent critic of the United States, added that if other military attaches were caught spying they could be detained.
"We have decided, in diplomatic terms, to declare him persona non grata, in plain Spanish that means to throw out of the country an officer at the US military mission for spying"
Correa's whereabouts were unclear. In Washington, a US Defence Department spokesman, Lieutenant Colonel Mark Ballesteros, said the officer "has been rotated back to the US mainland for further duties as assigned".
The US State Department denied that the attache had been involved in spying. "None of the attaches was or is engaged in inappropriate activities", said Janelle Hironimus, a State Department spokeswoman.
Hironimus said the US embassy in Venezuela had received a letter on Monday outlining accusations of espionage against the naval attache.
Another State Department official, who asked not to be named, confirmed the embassy had received a formal note on Thursday declaring Correa persona non grata.
Hironimus said Washington would react through diplomatic channels, but gave no indication what form that would take.
Chavez said on Monday that Venezuelan authorities had infiltrated a group of military officers from the US embassy who he alleged had been spying on his government.
Officials have said the network included some Venezuelan navy officers who were accused of passing sensitive information to Washington.
In his speech, Chavez called for a maximum 30 year jail term for those found guilty of aiding the United States. Chavez frequently accuses Washington of plotting against him and charged that the United States backed an aborted coup against him in 2002.
The Bush administration says Chavez is destabilising the region. It recently prevented Spain from selling military planes with US parts to Venezuela.