What part of speech is the word mistaken?

"Mistaken" can be either an adjective or a verb (past participle), depending on how it's used in a sentence.

Examples:

* Adjective: "You have a mistaken idea about what I do."

* Verb (past participle): "I mistaken him for my brother."

Let me know if you have a specific sentence in mind, and I can help you determine the part of speech!