The vehicle was recovered and six hours' worth of data downloaded.
"The data was analysed and no objects of interest were found," the statement said. "The vehicle is in good material and working condition."
The Bluefin-21 was to make a second mission to the remote Indian Ocean seabed when weather conditions permit.
The search for the missing plane could take up to two months as the underwater vehicle takes six times longer to cover the same area as the towed pinger locator, officials said.
"It is estimated that it will take the AUV anywhere from six weeks to two months to scan the entire search area," Lt J G Daniel S Marciniak, a spokesman for the US Seventh Fleet, said in a statement.
Malaysia's Acting Transport Minister Hishammuddin Hussein told reporters in Kuala Lumpur that it's "not important" who gets the black box, it is more important to find the truth.
Finding the black box is crucial to know what happened on March 8 before the Beijing-bound plane with 239 people, including five Indians, an Indo-Canadian and 154 Chinese nationals, mysteriously vanished after taking off from Kuala Lumpur.
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