The aim of this paper is to contribute to a better understanding of how prepositions are used. One of the grammatical features of contrastive analysis is preposition. In English there are more prepositions than in Persian. The contrastive analysis of this paper is focused on two English prepositions: "of" and "from." These prepositions are used in many situations, but most of the time the learners get confused. They don't know the correct usage in a context. This study defined the prepositions "of" and "from" based on two dictionaries. Understanding these definitions help EFL learners to decrease their mistakes in using this group of prepositions. As the study will show, their usage differs in certain contexts.