Most foreign speakers of a target language often produce ungrammatical utterances. In this paper I attempted to analyze and explain the errors made by Korean students learning Swedish at the Hankuk University of Foreign Studies. The corpus consists of written production in Swedish, because it is considered as more reliable than oral one. Grammatical categories with examples are largely classified into three parts: verb phrases, noun phrases and prepositions which often cause many difficulties for Korean learners. In syntatic sturcture of Swedish lots of errors are triggered by the violation of word order. Inaccuracy of the sequence of tense and omission of the finite verb in subordinate clauses are frequently found in the learners`` verb phrases. Regarding the noun phrases, the selection of definiteness and indefiniteness which are decisive factors for constituting the form and meaning of a noun phrase make also a considerable problem. Furthermore, Swedish prepositions are notorious not only for their diversity, but also in their usage. The causes of these deviant structures may be partly influenced by the learners`` mother tongue, Korean and partly by their first foreign language, English. However, a substantial part of the causes may come from the complexity in Swedish itself.