The present study examined the relations of maternal literate support instructions during parent--child joint writing to children's word reading and writing across 1 year among 95 4- and 5-year-old children from Korea. The whole episode of mothers individually teaching their children how to write words was videotaped, and a Korean scale of mothers' literate mediation of their children's writing was developed based on six cognitive strategies focusing on whole Gulja (Korean written syllable), visual strokes, letter, Gulja structure, and CV (consonant + vowel) and coda (final consonant of a syllable) subsyllabic units. Maternal literate support explained a significant amount of variance in children's word reading and writing concurrently and longitudinally across 1 year after controlling for children's age, nonverbal IQ, phonological and morphological awareness, rapid automatized naming and mother's education. In addition, children's coda phoneme awareness explained unique variance in word reading and writing concurrently and longitudinally. Results underscore the unique characteristics of Korean and the importance of Korean maternal literate support as a major factor in early literacy development.