It is commonly observed that Korean students tend to use the English conjunction so more often than any other English conjunction when expressing cause or reason in English. On the other hand, because is the conjunction of choice among native English speakers. This paper attempts to explain why Korean English learners have the tendency to use so over other conjunctions, and to analyze some of the similarities and differences in the use of Korean and English causal connectors. The findings of the study provide an empirical basis for the development of course design and teaching materials, especially for the development of courses in English writing for academic purposes.