What would you do if you knew for sure your professor plagiarized?

I would discuss this matter with them outside of the classroom-setting.

Lay out your case with them, stating your resources and references.

Try to avoid the certain (legal and otherwise) ramifications if they continue this.

this is funny because we deal with this question on a daily basis, except the other way around (with professors thinking that STUDENTS have plagiarized.)

do you mean that your prof plagiarized from students in his class, or other published materials?

if you want to call him to task for this its really quite simple; just email the offending material and the original it was plagiarized from to the dean. actually, do a mass mail and send it to ALL professors or anyone of consequence within the university. then it will be impossible to ignore and sweep under the rug. if you want to do it anonymously, make up a new yahoo email address on a public computer. I would probably do just that because i would fear consequences (maybe the prof gets fired, but maybe he has some friends on staff who remember it was YOU that got him busted).

you could also choose to keep it between you and him to raise your GPA, eh? ;) kidding, just kidding

http://www.goodtermpaper.com/

Would help to know the evidence you have against them. Usually professors don't have to write paper so they don't have to plagiarize, but if he is taking credit for his student's work or claiming stuff as his own then that is academic suicide and how can a teacher teach against doing it if they are doing it. I would go to the administration so that they could at least keep an eye on him and catch him in the act, but if you are going to accuse someone then you better have proof. if you have no proof then it is a theory and holds no water and you are just a student who doesn't like their teacher so they want them to lose their job.

If i knew for sure, i would probably try to find some of his former students and ask them if he has done it before and what to do about it. I wouldn't go and try to confront the professor unless no other choice but to

If I like him or her or if it's a good teacher nothing. If I don't like them or if he or she is a bad teacher then maybe I'll ask them about it or try to bring it up sometime. If it was a legitimate mistake I'd forget about it, but if he or she meant to I'd tell their boss. They don't deserve credit for copying someone else's work.

teachers give me some small works with other teacher's name on, so its not really something they try to cover.. if you are talking about something that goes further it depends but telling them is not really a good idea.

send a copy of his work and the original to the university authorities anonymously, it is the number one crime in academia

It depends what it was. But really, this is up to the school's administration to discover and to police, not you.

was it in a paper or a book or was it just in a lecture. if it was in a lecture, just ignore it. if it was in a book, talk to him about it.

report him

but only if your ONE HUNDRED PERCENT