This paper discusses an annotation scheme for Korean null pronouns, which were used in annotating three kinds of Korean text corpora including Penn Korean Treebank. In annotating the corpora, null pronouns and their antecedents were marked up for their type and reference, with coreference relation tracked by numeric identifiers. Based on the annotation scheme, an outline of a potential pronoun resolution strategy is also proposed. The resulting dataset of annotated text is rather small at 11,834 words; we hope the null pronoun classification and annotation scheme proposed in this study will serve as a basis in developing a large-scale annotated corpus in the future.