This research attempts to show the study of grammar which is limited only on the use of ellipsis as the way to omit the pieces of sentences in dialog. This study shows that the omission of parts occurs in dialog by applying ellipsis theory of Halliday (1994), Biber et al (1999) and Sinclair (ed.)(2000). This study uses sources of data from two American novels entitled The Relic by Evelyn Anthony and The Lonesome Gods by Louis L’amour. The analysis methods conducted in this study are (a) to analyze the use of ellipsis in dialog and explain the parts of the sentence that are omitted (b) to analyze the function of ellipsis and the effect in written language. This study finds that the use of ellipsis functions to minimize the conversation, to avoid the use of the same words and to omit the words that have been spoken in questions. This study also shows that ellipsis may make the sentence to be ungrammatical in standard language.