This Research and Development (R&D) aims to develop and test the effectiveness of a series of picture storybooks based on the local culture of Bogor in improving the expressive language skills of children aged 5-6 years. The research was conducted in Bogor Regency. The development focused on three main themes, namely traditional transportation, culinary specialties, and historical sites, which are expected to enrich children's vocabulary, cultural knowledge, and cognitive abilities. The development model used is Borg and Gall, through the stages of preliminary study, planning, initial product design development, small group testing (6 children), revision, large group testing (20 children), to the final product. Data was collected through needs questionnaires, observations, and teachers' reflective journals. The results of expert validation of the material and media showed that the “Bogor cultural picture storybook” product was deemed highly feasible. The results of the trial showed that this medium was effective in improving children's expressive language skills, as seen from the increase in the quantity and quality of their vocabulary, their fluency in storytelling, and their courage in expressing their opinions. The children became able to describe and recount cultural objects that they had not known before. The use of books as a guide in sociodrama activities also encourages increased creativity, self-confidence, and simple analytical skills. Thus, these locally-based picture storybooks are not only valid and appropriate, but also proven to be effective as an alternative contextual literacy medium for improving the expressive language skills of early childhood.