In this paper, we present a Question Answering system called KUQA (Korea University Question Answering system) developed by using semantic categories and co-occurrence density. Semantic categories are used for computing the semantic similarity between a question and an answer, and co-occurrence density is used for measuring the proximity of the answer to the words of the question. KUQA is developed based on the hypothesis that the words that are semantically similar to the question and locally close to the words a ppeared in the question are likely to be the answer to the question.