This paper examines the semantic and syntactic characteristics to the connective endings '-deoni' and '-eossdeoni'. It has been claimed in previous many studies and korean study books that they have the same meanings and syntactic constraints. But semantically, while '-deoni' indicates sequential, contrasting, supplementary and causal relation, '-eossdeoni' indicates sequential, reactive, discovering, contrasting, supplementary and causal relation. Also syntactically, two connective ending are different. First, '-eossdeoni' does not have a 'subject agreement constraint', while '-deoni' requires mostly a 'subject agreement constraint in the pre-clause and post-clause. Second, '-eossdeoni' has the first person, second person or third person's activity in pre-clause, but '-deoni' does not have the first person's activity in pre-clause. Third, while '-deoni' has the witness event of speaker or the speaker's feelings in pre-clause and post-clause, '-eossdeoni' has the activity of the first person or the second and third person in pre-clause, having of different person' activity in post-clause. Therefore, '-deoni' and '-eossdeoni' should be separate to the different connective endings and should be taught to korean learners. (Sungkyunkwan University)