两者都可表示“慢”，但slow通常只与少数动词(如 go, drive, pass, climb, run, walk 等)连用，且应置于其后；而slowly则用法较广，且可置于动词之前或之后，有时还可置于句首。
知识拓展
类似slow和slowly的词语还有：
（1）quick-quickly
She gave him a quick glance.
她迅速扫了他一眼。
These cakes are very quick and easy to make.
这些糕饼做起来又快又简单。
Would you like a quick drink?
你要不要小饮一杯？
The doctor said she'd make a quick recovery.
医生说她很快就能康复。
She walked quickly away.
她迅速走开了。
We'll repair it as quickly as possible.
我们会尽快把它修好的。
The last few weeks have gone quickly (= the time seems to have passed quickly) .
最近的几个星期过得很快。
（2）quiet-quietly
Tania kept the children reasonably quiet and contented.
塔妮娅把孩子们哄得安安静静而又心满意足。
She was received in a small, quiet office
她在一个安静的小办公室里受到接待。
'This is goodbye, isn't it?' she said quietly.
“这就算是告别了，是吗？”她轻轻地说。
He closed the door quietly.
他悄悄地关上了门。
（3）loud-loudly
The audience laughed loudly at the joke.
观众听到这笑话大笑起来。
Can you read the letter out loud?
你把信大声念一念行吗？
He laughed out loud at his own joke.
他对自己的笑话大笑起来。
One of them protests loudly, and the Americans cart him away in plastic handcuffs
其中有个人大声抗议，美国人就把他铐上塑料手铐带走了。