Floyd Mayweather is wasting no time unloading the hundreds of millions he won less than a month ago ... plunking down $25.5 million on a Beverly Hills mansion. 

The 15,000 sq ft home features 6 bedrooms, 10 bathrooms, a wine cellar and a guest house with a movie theater. The crib was built by developer Nile Niami and also features an incredible backyard pool for when Floyd wants some R&R.

We're told Floyd also bought the place fully furnished too ... so when all was said and done, the boxer paid a total of $26 million.

Floyd's been on a tear since taking down Conor McGregor ... he also spent a quarter million on Birkin bags during a shopping spree with hot chicks last week.

EASY LIVIN'
TMZSports.com