如果副詞是以 ly 結尾，就必須在副詞前加 more 來形成比較級，最高級則是在副詞前加 most。
| 副詞 | 比較級 | 最高級 |
|---|---|---|
| quietly | more quietly | most quietly |
| slowly | more slowly | most slowly |
| seriously | more seriously | most seriously |
舉例
- The teacher spoke more slowly to help us to understand.
- Could you sing more quietly please?
對於單音節、沒有 ly 字尾的副詞，其比較級和最高級的型態跟形容詞的規則是一樣的：在字尾加 er 即形成比較級，而在字尾加 est 即形成最高級。如果副詞字尾是 e，就先將它去掉，再加比較級或最高級字尾。
| 副詞 | 比較級 | 最高級 |
|---|---|---|
| hard | harder | hardest |
| fast | faster | fastest |
| late | later | latest |
舉例
- Jim works harder than his brother.
- Everyone in the race ran fast, but John ran the fastest of all.
有些副詞有不規則型態的比較級和最高級。
| 副詞 | 比較級 | 最高級 |
|---|---|---|
| badly | worse | worst |
| far | farther/further | farthest/furthest |
| little | less | least |
| well | better | best |
舉例
- The little boy ran farther than his friends.
- You're driving worse today than yesterday!
- He played the best of any player.