Research Findings: I examined the long-term association between the lexical and acoustic features of maternal utterances during book reading and the language skills of infants and children. Maternal utterances were collected from 22 mother-child dyads in picture book-reading episodes when children were ages 6-12 months and 5 years. Two aspects of language input were studied: "lexical features" (the amount and diversity of vocabulary, and the proportion of isolated target words) and an "acoustic feature" (the acoustic space of vowels). Standardized language tests were used to assess receptive vocabulary and language production abilities at age 5. The results showed that greater diversity of vocabulary and the use of fewer isolated target words during book reading with infants were associated with enhanced language skills in children 4 years later. Regression analyses showed that the proportion of isolated target words was the most potent predictor of, and acoustic vowel space also accounted for, variance in language expression skills at age 5. Maternal utterances and mothers' education jointly accounted for more than 60% of the variance in language abilities. Practice or Policy: These findings suggest that lexical and acoustic inputs in picture book reading with infants have long-term associations with children's language development throughout early childhood.