This paper investigated Korean heritage learners" acquisition of Korean as a second language. In particular, written narratives of 16 Korean heritage learners were analyzed in order to identify errors and strategies observed in Korean heritage learners" second language writing. The findings of the study indicated that learners" errors were not significantly related to their proficiency levels in the target language. Likewise, no significant differences were observed in errors due to their proficiency levels. However, some differences were noted in several grammatical categories. In case- or tense-related areas, learners with higher proficiency levels were not much more accurate than those with lower proficiency levels. However, in terms of the use of inflectional markers, learners with higher proficiency levels exhibited higher accuracy than lower level learners. With regard to their use of strategies, literal translation, code-switching, and approximation were most frequently observed in their writings. The paper concludes with some implications for teaching Korean as a foreign language.