This study aims to summarize shape, composition, meaning, and function of some prefixes copulative conjunctions(proword-conjunctions) /sentence copulative conjunctions/ (өгүүлбэрүүдийг зэрэгцүүлэн холбох үгс) in modern Mongolian language and make a contrastive analysis of them with Korean conjunctions based on some frequently used prefixes copulative conjunctions(proword-conjunctions)/sentence copulative conjunctions/ (‘Мөн түүнчлэн’, ‘Түүнээс гадна’, ‘Түүгээр ч барахгүй/Тэр ч байтугай/’, ‘Тэгээд’, ‘Тэгэхлээр’, ‘Тэгвэл’, ‘Тэгэхэд’, vТийм учраас’, ‘Хэдий тийм боловч’, ‘Яагаад гэвэл’). This study also looks at the similarities and differences by making a contrastive analysis and presents the right way to use conjunctions that appear important to learners of both languages in discourses or contexts and the base line data for this. Modern Mongolian prefixes copulative conjunctions (proword-conjunctions)/ sentence copulative conjunctions/ belong to Korean ‘sentence connecting adverb’, ‘conjunctive’, ‘conjunctive adverb’, and ‘conjunction’. Furthermore, both languages are similar in that there exist many conjunctions using some pronouns(그, 저, 이, .../тэр, энэ, түүн, үүн, ...) or verbs(그러하다, 그리하다, 이러하다, 이리하다, .../тийм болох, тэгэх, ингэх, гэх, ...) among conjunctions from both languages and that these conjunctions are largely used in the front area of rear sentences to connect front sentence and rear sentence. On the other hand, both languages are different in that Mongolian language acknowledges the category of independent part of speech called as conjunction and that Korean language deals with sentence connecting adverb, conjunctive, conjunctive adverb, and conjunction within the sub category of adverb rather than within the independent category. In addition, these conjunctions are largely used to connect short sentences in Korean language, whereas such conjunctions are used to connect more than two clauses within one sentence(compound sentence) in Mongolian language. At this time, the predicate of verb in the antecedent clause takes a limited connective suffix and uses comma(,) at the end. In Korean language, connective endings are largely responsible for such a role. In both languages, particular conjunctions are not used as having one meaning or function, but rather can be used in various meanings depending on the context. Thus, it seems to be necessary to identify the meanings within sentence or context and select appropriate conjunctions and corresponding forms. Recently, the exchange between Korea and Mongol is expanding rapidly in various fields and accordingly the number of learners who desire to acquire both languages is increasing rapidly. In this situation, what we need to pay attention to is above all expression of opinions, in other words, communication. Therefore, it seems to be necessary to take a continuous interest in conjunctions from both languages (Korean and Mongolian) which play an important role in improving appropriate expression of opinions, in other words, communication and conduct a steady research.