Huckleberry Finn was banned at first within a month of its release. It was said to be "Not suitable for trash" according to librarians in Concord Massachusetts. This happened in the year of 1885, and since then this book has been banned and had other troubles various times.
Why did this book have so many problems? Some say that it was due to the fact that is used the N-word in it. Another reason is that Jim, in the novel, is a stereotype according to some people, People feel as if he's put down during the book and later Huck feels guilty for assisting Jim in getting free.
The activities of the main character are referred to as "coarse" and that's because he steals, rebels against authority figures, speaks badly, and even runs away from his home.
Then there's the fact that back when this book was released, some people wanted it to be banned because it showed a white boy being a friend with a slave. Needless to say, this book has been through a lot and was very controversial!
1 - http://www.pen.org/nonfiction/mark-twains-huckleberry-finn
2 - http://www.brighthubeducation.com/homework-help-literature/54471-should-huckleberry-finn-be-banned/