The purpose of this study is to review the composition of Korean connectives ‘-deoni’ and ‘-eossdeoni’. The seeming difference between ‘-deoni’ and ‘-eossdeoni’ is just the existence of the pre-final ending ‘-eoss-’, but there is a difference between these two connectives. We reviewed the composition of ‘-deoni’ and ‘-eossdeoni’. There are many disputes in the linguistic research of the Korean language over the construction of ‘-deoni’ and ‘-eossdeoni’. This can be summed up in two ways. One is that ‘-deoni’ and ‘-eossdeoni’ can be seen in the form of <‘-deo-’+‘-(e)ni’> and <‘-eoss-’+‘-deoni(‘-deo-’+‘-(e)ni’)’>, respectively, and the other is that ‘-deoni’ and ‘-eossdeoni’ can be seen as one independent form that can no longer be separated. The result is that ‘-deoni’ includes ‘-deo-’, but there is a difference in the usage of ‘-deoni’ and ‘-eossdeoni’ and they should be viewed as an independent form. The difference between ‘-deoni’ and ‘-eossdeoni’ can be seen as the result of the existence of ‘-eoss-’; therefore, this is the evidence of the formation of ‘-eossdeoni’ as a <‘-eoss-’+‘-deoni’>. However, there are differences in the usage of ‘-eossdeoni’ and ‘-deoni’, which are the evidence of taking ‘-eossdeoni’ as an independent form.