The Ultimate Encyclopedia of BOXING by Harry Mullan claims the longest unbeaten streak is Hal Bagwell.105-8 (183) 1938-48, Gloucester, UK. Boxrec shows his streak at 65-0-4. Packey Mc Farland (97) 1905-15, Chicago, IL, Boxrec shows a record of 107-1-5 and 70-0-5.
Pedro Carrasco (93), 1964-71, WBC Light Champion from Huelva, Spain. A former European champion. He won the title WDQ12 over Mando Ramos, 31-4, then lost back-to-back fights to Ramos.
Middleweight and welterweight champion ‘Sugar’ Ray Robinson (91), 1943-51. He was 89-0-2. Robinson won his first 40 fights before losing to middleweight champion Jake ‘Bronx Bull’ LaMotta 30-5-2. Five fights later, he defeated LaMotta for the title. He defeated LaMotta in 4 out of 5 fights.
Robinson was 129-1-2 when he lost to Randy Turpin, 40-2-1, in London, UK, July 1951. Two months later, in September at the New York Polo Grounds, he defeated Turpin in 10 rounds. Five fights after losing to Turpin, he defeated Henry ‘Homicide Hank’ Armstrong 132-17-8, who held the featherweight, welterweight and then lightweight titles simultaneously. Of course, Armstrong was a former champion past his prime and possibly the second best P4P boxer after Robinson.
More in the modern era was WBO, IBF and WBA super middleweight champion Joe Calzaghe of Wales, who came to the US 44-0 and defeated former champion Bernard Hopkins 48-4-1, who was another other world would win championship. Then he defeated former champion Roy Jones, Jr., 52-4, who was past his prime and neither man ever fought again. Calzaghe struggled with his hands, which caused his retirement. He became a unified champion, defeating Denmark’s WBA and WBC champion Mikkel Kessler 39-0 in the previous fight before Hopkins.
Mexico’s Julio ‘JC’ Chavez, 107-6-2, was 89-0-1 when he first faced
Frankie ‘The Surgeon’ Randall, 48-2-1. He would defeat Randall in the rematch. He was 96-1-1 when he lost to Olympic gold medalist Oscar De La Hoya 21-0.
Of course, two champions who retired undefeated were heavyweight champion Rocky Marciano, 49-0, and multi-division champion Floyd ‘Money’ Mayweather, 50-0. Today, the undefeated with the most wins is former two-time world division champion Terence ‘Bud’ Crawford at 40-0. Current Light Heavyweight Champion Gilberto ‘Zurdo’ Ramirez, who lost 44-0 to Dimitrii Bivol, then 20-0.
There you have it for the most winning boxers. Now let’s take a brief look at the boxers who lose the most. Kristian Laight, of the UK, 12-279-9, with the most losses. Still active is Fonz Alexander, 9-167-1, of the UK, currently tied for eleventh most losses.
The worst record is Bheki ‘Black Tiger’ Moyo, 0-73-2, of Zimbabwe and the UK. He retired in 2015. Miguel Urdaneta, 0-37-1, is still active in Venezuela. Also active are Jake Pollard, 1-80, of UK, Ganadij Krajevskij, 1-74, of Lithuania and UK, and Jake Osgood, 1-61, of UK.
There you have it, boxing fans, the winningest and the losingest boxers.
 1938-48, Gloucester, UK. Boxrec shows){kind=link}