Here are 4 fighters that went undefeated in their entire career, that I know of:

-Jack McAuliffe 33-0-9 and 3 no contests
-Rocky Marciano 49-0
-Laszlo Papp 27-0-2
-Ji Won Kim 16-0-2

If anybody else that know of any other fighters that went undefeated in their careers, feel free to add or correct.

Ricardo `Finito` Lopez......I am sure retired undefeated....Also Floyd Mayweather if he sticks to his promise....

golden boy is right. Ricardo Lopez retired undefeated in 2001, 51-0-1, 38 ko

Got another one for you, Sven Ottke........German Super middleweight.....34-0

UNDEFEATED BOXERS

1. Jimmy Barry - World Paperweight Champion (110lbs) - 58 (38) - 0 (0) - 10
2. Samson Dutch Boy Gym - WBF Super Flyweight Champion - 43 (36) - 0 (0) – 0
3. Jemal Hinton - WBC Continental Americas Super Bantamweight Champion - 22 (17) - 0 (0) – 0
4. Ike Ibeabuchi - WBC International Heavyweight Champion - 20 (15) - 0 (0) - 0
5. Ji Won Kim - IBF Super Bantamweight Champion - 16 (7) - 0 (0) - 2
6. Michael Loewe - WBO Welterweight Champion - 28 (10) - 0 (0) - 0
7. Ricardo Lopez - IBF Light Flyweight Champion - 51 (38) - 0 (0) - 1
8. Rocky Marciano - World Heavyweight Champion - 49 (43) - 0 (0) - 0
9. Terry Marsh - IBF Light Welterweight Champion - 26 (10) - 0 (0) - 1
10. Jack McAuliffe - World Lightweight Champion - 34 (23) - 0 (0) – 5
11. Young Mitchell – American Featherweight, Australian Lightweight, PC Welterweight, and PC Middleweight Claimant - 35-0-6 (BoxRec only has 5-0-4)
12. Edson Pedro Nascimento - UBC Ibero-American Lightweight Champion - 47 (40) - 0 (0) - 1
13. Horace Notice - Commonwealth (BE) Heavyweight Belt-holder - 16 (12) - 0 (0) - 0
14. Sven Ottke - WBA & IBF Super Middleweight Champion - 34 (6) - 0 (0) - 0
15. Laszlo Papp - EBU (European) Middleweight Champion - 27 (15) - 0 (0) - 2
16. Pichit Sitbangprachan IBF Flyweight Champion 24 (18) - 0 (0) – 0
17. Mzukisi Skweyiya - South African Non-White Bantamweight Champion - 21 (7) - 0 (0) – 1


Here's some others that were Undefeated:

1. Kirk Daley - (1988-1994) Former Jr. Middleweight Contender - 19 (18) - 0 (0) - 0
2. Scott Daley - (1986-1998) Former Middleweight Contender - 24 (24) - 0 (0) - 0
3. George Kandelaki - (1998-2003) Former Heavyweight Contender - 24 (18) - 0 (0) - 0
4. Vinny Letizia - (1990-1993) Former Welterweight Contender 16 (14) - 0 (0) - 1
5. Tom Gleason - (1890-1896) Middleweight Champion of North & South Dakota, & Montana - 6-0-3 (2 ND)
6. Niels H Madsen – (1990-1992) Former Cruiserweight 8 (4) - 0 (0) - 0
7. Agustin Senin – (1967-1972) Spanish & EBU (European) Bantamweight Champion - 42 (21) - 0 (0) – 1
8. Gurcharan Singh (2001-2004) Former Cruiserweight 17 (10) - 0 (0) - 0
9. Jimmy Wilde (Moisés Ortenberg) - (1935-1943) Argentina - 37 (15) - 0 (0) - 5
10. Ricky Womack – (1984-2001) (defeated Holyfield 3 times in the amateur) 13 (6) - 0 (0) - 1

I have a lot more too!