The purpose of this study is to analyze the aspects and causes of errors in Chinese Korean Learners’ use of the object particle ‘eul/reul’(을/를). The research was based on a large scale learner’s corpus. The study focuses on examing the following three aspects: 1) the development of error changes according to the learners’ Korean ability, 2) the cause of errors, and 3) substitution errors due to L1 interference. Of the 2,856 objective particle errors, substitution errors consisted of about 68% of the errors. It is worth noting that as the learners’ Korean abilities increased, so too did the rate of error, while the rate of substitution errors increased at a more gradual rate as learners’ fluency increased. In the analysis of the cause of errors, the results will confirm that intrusive interlingual interference caused an increase in error rates 42% substitution errors were due to the influence of the learners’ L1. These results can be interpreted to signify that L1 interference emerges more frequently as fluency increases. In the analysis of substitution errors, the subject particle, ‘i/ga’(이/가), was used in place of the object particle ‘eul/reul’(을/를) most often; mainly in the case of particles followed directly by predicates. As for other particles that substituted the objective ‘erl/reul’(을/를), the forth meanings of ‘erl/reul’(을/를) do not have the ‘V+Obj.’ sentence structure in Chinese. This study is to serve as an explanation of Chinese Korean learners’ objective case ‘eul/reul’(을/를) errors, as well as to help in researching pedagogical methods for these learners. (Namseoul University)