An apparatus for detecting grammatical errors includes a sentence analyzer to break up a sentence into units of morphemes, tag the morphemes with parts of speech, and analyze a syntactic structure of the sentence based on the tagged parts of speech; a first error detector to generate part-of-speech sequences using n-grams of the tagged parts of speech, and detect first grammatical errors by analyzing the generated part-of-speech sequences based on grammatical rules; a second error detector to generate morpheme sequences by binding the morphemes in a preset window (n-window) size, and detect second grammatical errors according to frequencies of appearance of morpheme sequences identical to the generated morpheme sequences by searching examples from an example-based index database (DB); and an integrated error detector to determine final grammatical errors in the sentence by combining the detected first grammatical errors and the detected second grammatical errors.