Methods and systems for extracting sentences are provided, one of methods comprises, receiving a keyword, parsing a document, and identifying each of a plurality of sentences included in the parsed document, configuring a graph having vertices and edges, wherein each vertex corresponds to each sentence, and each edge has a first weight corresponding to similarity between each pair of the sentences, calculating importance of each sentence by applying a modified PageRank algorithm to the graph, wherein the modified PageRank algorithm is designed to reflect a second weight corresponding to whether the keyword is included in a sentence of each vertex adjacent to a first vertex and extracting important sentences from the document based on the calculated importance.