Mayweather began his sentence on schedule in a domestic battery case, USA Today reported.
The boxer had pleaded guilty Dec. 22 to a reduced domestic battery charge in a case involving Josie Harris, the mother of his children.
Mayweather was sentenced to the Clark County Detention Center in Las Vegas. He could receive time off for good behavior, officials said.
A police spokesman said Mayweather will spend his first week in administrative isolation for his own protection.
The Nevada Athletic Commission said Mayweather may reapply for his boxing license after completing his jail sentence and his required 100 hours of community service and domestic violence counseling sessions.