The present study investigated the associations of Korean mothers' attention regulation and referential speech during play with their toddlers' language and play development. The play interaction between mothers (n = 42) and their toddlers aged between 13 and 23 months was videotaped during home visits. Maternal behavior in regulating their toddlers' attention was coded from videos as introducing, redirecting, or following. Mothers' referential speech during joint attention with their toddlers was transcribed and classified as simple, elaborative, or prompting. Toddlers' expressive and receptive vocabulary sizes were reported by mothers. Their exploratory, functional, and symbolic play was coded from videos. Results showed that mothers' attention following and elaborative referential speech were associated with larger expressive vocabulary sizes and frequent symbolic and functional play in 1-year-olds. By contrast, mothers' attention redirection as well as simple and prompting referential speech were associated with toddlers' smaller expressive vocabulary sizes and less frequent functional play. After controlling for child age, maternal elaborative referential speech made an additional contribution to toddlers' decreased functional and increased symbolic play that was above and beyond the effect of maternal attention regulation. These findings replicated and extended previous research in Western cultures and underscored the role of maternal attention regulation and referential speech in toddlers' language and play development. (Contains 5 tables.)