Word formation is a process of creating new words by using existing words. Word formation can be found in daily communication, or in the literary works such as the novel. In this paper, the writer found 340 words which have word formation process with the frequency of appearance 755 times in chapter sixteen of Harry Potter and the Sorcerer's Stone novel written by J. K. Rowling. From 340 words which have word formation process, it is classified into five word formation types. They are inflection, a process that adds grammatical information to existing words; suppletion, a total change of the root of words; derivation, a process that uses affixes to create new words with different meaning and/or category from its base; cliticization, a process of a word becomes a clitic; and compounding, a process of creating new words by combining two or more existing words. In the result of this paper, inflection is the word formation types that mostly found because the infection can be said as a productive way to create a new word.