In this study, we investigated the role of cultural identity in self-assessment of heritage language skills for Korean heritage speakers in the U.S. The influence of a language domain i.e., speaking vs. writing, on self-assessment outcomes was also examined. Thirty Korean- American participants completed questionnaires on their language background, cultural identity, and self-rating of Korean speaking and writing skills. Speech and writing samples in Korean were then elicited with picture stimuli. Results of the self-assessment were closely related, but not identical, to those of the formal assessment, which suggests the potential of self-assessment as a complementary assessment tool in heritage language learning to provide information not obtained from other traditional types of assessment. In addition, bicultural identity was a strong predictor for self-assessment of speaking and writing in Korean. While the heritage speakers’ reported language exposure before age 5 and current patterns of language use predicted the self-assessment of speaking, the quality of output from external assessment was a strong predictor for the self-assessment of writing in Korean.