如果副词是以 ly 结尾，就必须在副词前加 more 来形成比较级，最高级则是在副词前加 most。
| 副词 | 比较级 | 最高级 |
|---|---|---|
| quietly | more quietly | most quietly |
| slowly | more slowly | most slowly |
| seriously | more seriously | most seriously |
举例
- The teacher spoke more slowly to help us to understand.
- Could you sing more quietly please?
对于单音节丶没有 ly 字尾的副词，其比较级和最高级的型态跟形容词的规则是一样的：在字尾加 er 即形成比较级，而在字尾加 est 即形成最高级。如果副词字尾是 e，就先将它去掉，再加比较级或最高级字尾。
| 副词 | 比较级 | 最高级 |
|---|---|---|
| hard | harder | hardest |
| fast | faster | fastest |
| late | later | latest |
举例
- Jim works harder than his brother.
- Everyone in the race ran fast, but John ran the fastest of all.
有些副词有不规则型态的比较级和最高级。
| 副词 | 比较级 | 最高级 |
|---|---|---|
| badly | worse | worst |
| far | farther/further | farthest/furthest |
| little | less | least |
| well | better | best |
举例
- The little boy ran farther than his friends.
- You're driving worse today than yesterday!
- He played the best of any player.