Mayweather failed to meet the deadline last Friday for paying the $200 000 sanctioning fee required by the WBO.
The American took the belt from Pacquiao in Las Vegas on May 2 in the richest fight in history, earning a reported $220 million.
WBO rules require boxers to pay three percent of their purse to fight for a world title up to a maximum of $200 000.
The rules also prohibit WBO champions to hold any belts in any other weight divisions. Mayweather is also the WBC and WBA champion at super-welterweight (69.85 kg) and welterweight (66.68 kg).
A statement on the Puerto Rico-based sanctioning body's website confirmed that Mayweather, regarded as the best boxer, pound for pound, in the world, was no longer the WBO champion.
The statement said Mayweather failed to pay the $200 000 fee required of him “as a participant of a WBO world championship contest.
"Despite affording Mr Mayweather the courtesy of an extension to advise us of his position within the WBO welterweight division and to vacate the two [69.85kg] world titles he holds, the WBO … received no response from him or his legal representatives on this matter.
"The WBO world championship committee is allowed no other alternative but to cease to recognize Mr Mayweather as the WBO welterweight champion of the world and to vacate his title."
After Mayweather, whose record stands at 48-0, with 26 knockouts, defeated Pacquiao to unify three of the four welterweight titles, he declared he would vacate all his titles to give younger fighters the chance to win belts.
"I don't know if it will be Monday or maybe a couple weeks," Mayweather said at the post-fight news conference. "I'll talk to my team and see what we need to do. Other fighters need a chance."
American Timothy Bradley, who defeated countryman Jessie Vargas for the WBO interim welterweight belt on June 27, is expected to be formally elevated to full champion status.
[H/T: Supersport]
