This study aimed to examine the influence of the complexity of the story-book on caregiver extra-textual talk (i.e., interactions beyond text reading) during shared reading with preschool-age children. Fifty-three mother-child dyads (3;00-4;11) were video-recorded sharing two ostensibly similar picture-books: a simple story (containing no false belief) and a complex story (containing a false belief central to the plot, which provided content that was more challenging for preschoolers to understand). Book-reading interactions were transcribed and coded. Results showed that the complex stories facilitated more extra-textual talk from mothers, and a higher quality of extra-textual talk (as indexed by linguistic richness and level of abstraction). Although the type of story did not affect the number of questions mothers posed, more elaborative follow-ups on children's responses were provided by mothers when sharing complex stories. Complex stories may facilitate more and linguistically richer caregiver extra-textual talk, having implications for preschoolers' developing language abilities.