As fighters developed multiple skills and masters of single disciplines gave way to multi-disciplined athletes, it became necessary to develop weight divisions. As in boxing, it is unsafe and unfair to match equally talented competitors of drastic strength differences together in competition.
The lightweight division (less than 170 pounds) was added at UFC 16 on March 13, 1998. It was not until UFC 31 (May 4, 2001) that many weight divisions were instituted as a result of the New Jersey State Athletic Control Board involvement in developing uniform UFC rules. The new weight divisions are:
| Flyweight |
Under 125 pounds |
| Bantamweight |
125-134.9 |
| Featherweight |
135-144.9 |
| Lightweight |
145-154.9 (Jens Pulver ) |
| Welterweight |
155-169.9 (Carlos Newton) |
| Middleweight |
170-184.9 (Title Open) |
| Light Heavyweight |
185-204.9 (Tito Ortiz) |
| Heavyweight |
205-264.9 (Randy Couture) |
| Super Heavyweight |
over 265
|
