List of undefeated boxing world champions

Boxer
Record
Weight class
Title(s)
Championship years
Title defenses
Notes
United States Jimmy Barry
59–0–9 (2)
Bantamweight
World
1894–1899
6 (3 draws)
-
United Kingdom Joe Calzaghe
46–0–0 (0)
Super middleweight
WBO
1997–2008
21
Vacated title to move up to light heavyweight.
United Kingdom Joe Calzaghe
46–0–0 (0)
Super middleweight
IBF
2006
1
Vacated title to fight Peter Manfredo Jr. instead of #1 contender Robert Stieglitz.
United Kingdom Joe Calzaghe
46–0–0 (0)
Super middleweight
The Ring, lineal
2006–2008
3
Vacated titles to move up to light heavyweight.
United Kingdom Joe Calzaghe
46–0–0 (0)
Super middleweight
WBA, WBC
2007–2008
0
Vacated titles to move up to light heavyweight.
United Kingdom Joe Calzaghe
46–0–0 (0)
Light heavyweight
The Ring
2008
1
Retired and vacated title.
South Korea Kim Ji-won
16–0–2 (0)
Super bantamweight
IBF
1985–1986
4
-
Romania Mihai Leu
28–0–0 (0)
Welterweight
WBO
1997
1
Retired from boxing due to an injury.
Mexico Ricardo López
51–0–1 (0)
Minimumweight
WBC
1990–1998
22
Vacated title to move up to light flyweight.
Mexico Ricardo López
51–0–1 (0)
Minimumweight
WBO
1997–1998
0
Unified WBC and WBO titles. Stripped of WBO title for saying he wanted to give the belt to his father.
Mexico Ricardo López
51–0–1 (0)
Minimumweight
WBA
1998
0
Vacated title to move up to junior flyweight.
Mexico Ricardo López
51–0–1 (0)
Light flyweight
IBF
1999–2002
2
-
United States Rocky Marciano
49–0–0 (0)
Heavyweight
World
1952–1956
6
-
United Kingdom Terry Marsh
26–0–1 (0)
Light welterweight
IBF
1987
1
Retired from boxing due to epilepsy.
United States Floyd Mayweather Jr.
50–0–0 (0)
Super featherweight
WBC
1998–2002
8
Vacated title to move up to lightweight.
United States Floyd Mayweather Jr.
50–0–0 (0)
Lightweight
WBC
2002–2004
3
Vacated title to move up to light welterweight.
United States Floyd Mayweather Jr.
50–0–0 (0)
Light welterweight
WBC
2005–2006
0
Vacated title to move up to welterweight.
United States Floyd Mayweather Jr.
50–0–0 (0)
Welterweight
WBA, WBC
2006–2008, 2011–2015
8
Retired at 49–0 in 2015; returned in 2017 for non-title McGregor fight and then retired again.
United States Floyd Mayweather Jr.
50–0–0 (0)
Light middleweight
WBA, WBC
2007, 2012–2015, 2017
2
Retired at 49–0 in 2015; returned in 2017 for non-title McGregor fight and then retired again.
Republic of Ireland Jack McAuliffe
30–0–5 (1)
Lightweight
World
1886–1893
7–0–2 (0)
-
Germany Sven Ottke
34–0–0 (0)
Super middleweight
IBF
1998–2004
21
-
Germany Sven Ottke
34–0–0 (0)
Super middleweight
WBA
2003–2004
4
Defended IBF title and defeated WBA champion to become WBA Super champion.
Russia Dmitry Pirog
20–0–0 (0)
Middleweight
WBO
2010–2012
3
Retired from boxing due to chronic back injuries.
Namibia Harry Simon
31–0–0 (0)
Light middleweight
WBO
1998–2001
4
Vacated title to move up to middleweight.
Namibia Harry Simon
31–0–0 (0)
Middleweight
WBO
2002
0
Won WBO interim middleweight title in 2001 and the outright title in 2002. Stripped of title at 22–0 when he was unable to defend it due to injuries suffered in a car crash.
Thailand Pichit Sitbangprachan
24–0–0 (0)
Flyweight
IBF
1992–1994
5
Retired at 21–0 and then made a comeback.
Venezuela Edwin Valero
27–0–0 (0)
Super featherweight
WBA
2006–2008
4
Vacated title to move up to lightweight.
Venezuela Edwin Valero
27–0–0 (0)
Lightweight
WBC
2009–2010
2
Vacated title to move up to light welterweight. Committed suicide after allegedly killing his wife in 2010.
United States Andre Ward
32–0–0 (0)
Super middleweight
WBA
2009–2015
6
Vacated titles in 2015 to move up to light heavyweight.
United States Andre Ward
32–0–0 (0)
Super middleweight
WBC, The Ring, lineal
2011–2015
1 (WBC), 2 (The Ring, lineal)
Vacated titles in 2015 to move up to light heavyweight.
United States Andre Ward
32–0–0 (0)
Light heavyweight
WBA, WBO, The Ring, lineal
2016–2017
1 (WBA, IBF, WBO), 0 (The Ring, lineal)
-

Question: What is Floyd Mayweather's Jr.'s overall career record, and in how many weight classes did he earn world titles?
Answer: In Floyd Mayweather Jr.'s career, he held multiple world titles in five weight classes (twice at welterweight) and retired with an undefeated record.