Throughout the history of SLA research, one of the first ways in which researchers tried to investigate L2 acquisition was through the analysis of learner errors (Ellis, 1994, p. 19). Studying learners`` errors is significant in order to understand the nature of the language learning process and to improve pedagogy. The present study aims at investigating characteristics/patterns of Korean EFL learners`` written productions through error analysis and providing effective methods of teaching English. The subjects were six Korean EFL college students currently enrolled in a two-year college in Korea. The data was collected through a writing assignment (Topic: Introduce yourself) given at the beginning of the semester. The results of the analysis indicate that (i) As for error frequency, young adult low-intermediate Korean EFL learners frequently made errors in determiners (mostly, indefinite articles), use of vocabulary (mostly, semantic errors). prepositions, and number (mostly, substitution of singulars for plurals). However, morphological elTors take a minor portion. The learners hardly make en``ors in attaching morphemes once they realize they need to add them: (ii) In relation to error source, many errors found in the data were caused by the habit of Ll use (i.e., Ll transfer). Especially, mis-use of vocabulary including overextension of the meaning seems to be a serious problem. It implies that teachers need to focus on instructing the usage of vocabulary rather than emphasizing the syntactic structure too much. Also. learners are encouraged to practice the usage of the words/phrases "in sentences" rather than through simple memorizations of individual words.