This study aimed to examine the role of L1 in the acquisition of L2 by comparing the acquisition of the three spatial prepositions (in, on, at) in English by native speakers of Russian and Turkish. The study, adopting a comparative approach suggested by Jarvis (2000, Methodological rigor in the study of transfer: Identifying L1 influence in the interlanguage lexicon. Language Learning 50. 245-309), compared interlanguages of L2 learners with Russian and Turkish L1 backgrounds, and examined the interlanguages of the L2 learners in relation to their native languages. The data for the analysis were collected via utilizing two diagnostic tests and analyzed quantitatively and qualitatively. The findings demonstrated that that the acquisition of the prepositions differed not only quantitatively but also qualitatively between the groups. The study adds to the comparative research examining the role of L1s in the acquisition of L2 and the effect of cross-linguistic influence taking place from background languages.