THE USE OF PREPOSITIONS IN SECOND LANGUAGE ACQUISITION PROCESS This thesis investigates the use of three most frequent prepositions by Turkish learners of English at intermediate level of proficiency. The aim of the present study is to find out which differences between prepositions and their corresponding postpositions or case suffixes constitute difficulty on the part of second language learners. This study also examines the possible reasons of the errors/ mistakes pertaining to &lsquo / in&rsquo / , &lsquo / on&rsquo / , &lsquo / at&rsquo / by native speakers of Turkish with intermediate level of proficiency in English. To fulfill the purpose of the study the participants of the study were recorded in natural classroom environment and the recorded data were transcribed. The compiled corpus was examined by two native speakers of English and the researcher. The data was classified under four main categories for each preposition inquired: (i) correct usage, (ii) misuse (i.e., instead of &lsquo / on&rsquo / , for instance, students use &lsquo / in&rsquo / or &lsquo / at&rsquo / e.g., in television ), (iii) overuse (i.e., no preposition is required in the context but the students use one, e.g., I am going at home now), (iv) omission (i.e., a preposition is needed but the students do not use one, e.g., We go holiday). At the end of these analyses, the problematic contexts related to the use of the prepositions &lsquo / in&rsquo / , &lsquo / on&rsquo / , &lsquo / at&rsquo / for TIME and PLACE were identified. For detailed analysis of each category two tools - the Statistical Package for the Social Sciences (SPPS) and the Computerized Language Analysis Child Language Data Exchange System (CLAN CHILDES) were used. Results indicate that Turkish learners of English produce erroneous forms of prepositions in second language acquisition process and the underlying reasons of these errors/mistakes is the interference of native language.