একটি Principal clause এবং এক বা একাধিক sub-ordinate clause নিয়ে গঠিত Sentence-কে Complex Sentence বলে।
Example:
He said that he was innocent.
This is the act that a wise man does.
If you read, you will learn.
[Note: If, although, though, before, after, as, because, since, that, so that, unless, whether, when, where প্রভৃতি দ্বারা complex sentence যুক্ত হয়।