Research Findings: The purpose of this study was to examine mothers' sophisticated vocabulary while reminiscing with their preschool-aged children, and its relation to children's story comprehension. The study used a cross-lagged panel design in which all assessments were collected twice, 6 months apart. We also compared two methods of examining sophisticated vocabulary -- rare words (i.e., words not on the Dale-Chall list) and word tiers (i.e., Tier 2 and Tier 3 words). We found that mothers' rare words predicted children's later story comprehension controlling for children's age, mothers' education, and children's receptive vocabulary. Mothers' Tier 3 words were related concurrently to children's story comprehension at time 2. Children's story comprehension did not predict mothers' later sophisticated vocabulary suggesting that this is not a bidirectional relation. Reasons for why mothers' sophisticated vocabulary input in the context of reminiscing might matter to children's story comprehension are discussed. Practice or Policy: These results suggest that researchers and educators may wish to examine the impact of vocabulary instruction on story comprehension in pre-readers in addition to vocabulary outcomes given the importance of early narrative comprehension to later reading comprehension.