This paper deals with the question of translating the Korean bound noun ``kes`` into Spanish. This bound noun plays several syntactic-semantic roles and each of them must be realized as a different form in Spanish. However, a lot of Korean students tend to consider the free relative pronoun ``lo que`` as the only counterpart of ``kes``. Owing to this, the error rate is very high, which is predicted by the grammatical hierarchy in six categories of difficulty(Prator, 1967). Thus, the aim of this paper is to provide a practical solution to this problem. Firstly, we present several syntactic-semantic roles that ``kes`` plays in Korean. Secondly, we show six most common errors. Thirdly, we analyse the causes of each error and then claim that ``kes`` can be translated as ``lo que`` only if it appears in free relative clauses. Finally, we provide some practical solutions which can be used helpfully to prevent or reduce errors.