Negation in modern Mongolian was analyzed by scholars namely: Luvsanvandan Sh (1968, 2000), Wonsoo Yu (1991), Mönkh-Amgalan Yu (1998), Purev-Ochir B. (1998, 2001), Byambasan P. (2006), Kunihiko Hasimoto (2008), BatIreedui J.(2009), Ravdan E. (2009), Mönkh-Amgalan Yu & Kan Shin (2014). Sentential negation in modern Mongolian is not sufficiently studied in sentential and discourse levels. The tendency of modern linguistic requires us to conduct more comprehensive and deeper research than previous scholars did. Our research is considered to be the first intended research on negation in modern Mongolian, because it is one part of Ph.D dissertation on negative meaning of modern Mongolian. There are two forms of sentential negations in modern Mongolian language, namely: explicit and implicit. Explicit negation is expressed by negative markers, but implicit negation is expressed by forms without negative markers, positive forms, intonations, structures with interrogative words and phrases. Negative markers have preverbal and postverbal positions in sentences. Preverbal negative markers are all particles ("büü," "bitgij," "ül," "es," "alga") and have SONegV sentential type, but postverbal negative markers are particles ("ügüj," "biš," "bus") and negative grammatical morphemes ("-güj," "-údzaj2," "-lgüj," "-ltgüj," "-mgüj," "-šgüj") which have SOVNeg type. Particles, which are used as preverbal and postverbal negative markers in modern Mongolian, have more specific features than negative markers in other languages. Their unique features are to be used not only as negative markers in negative sentences, but also to substitute for verb phrases in c-command and sentences in the discourse level. This paper aims to consider how sentential negative markers in modern Mongolian are used as pro-forms of negative sentences.