This paper seeks to analyze from the perspective of the interlanguage theory the transitional constructions that Chinese lerners of the Korean language acquire through the use of nominative and accusative case markers and suggests the pedagogical solution to prevent fossilization of interlanguage. The data presented in this paper shows that Chinese learners acquire the case marking system in Korean by means of universal grammar that encompasses case concept. However, the ommission of case marking is a phenomenon that occurs due to the under-development of spontaneousness that is required in applying the case marking principle. Thus, it is suggested that the teaching material include a solution that encourages learners to apply the principle of case-marking spontaneously. Moreover, this paper finds that the errors of replacing nominative case with accusative case is due to a transitional construction which is acquired when the learners have not yet recognized that some intransitives (i.e. ergative verbs) have only one argument that generates at the object position in the underlying structure but realizes at the subject position in the surface structure. Thus, it is important for the teaching material to encompass not only the distinction between transitives and intransitives, but also that between ergative intransitives and unergative transitives. Lastly, in order to understand the errors that replaces accusatives with nominatives, this paper analyzes the characteristics that the student has not yet learned to distinguish whether the complex verbal phrases are constructed by incorporation of verbal heads or by clausal incorporation. Thus, in order to avoid fossilization of transitional constructions of case marking in Korean, it is important to include the grammar education that accounts for the constructional difference of the complex verbal phrases.