Social robots are autonomous entities able to engage humans at the emotional and social level. They are being used in several domains, especially in those where kids are the primary users (i.e., education, games, rehabilitation). The paper presents an experience in which the social robot Pepper is used as a storyteller. A storyteller robot should engage humans by combining its verbal and non-verbal behaviors and ‘immerse’ the user into the story. Therefore, to design an engaging and effective storytelling experience we started to address a first design issue: does a human voice have an advantage over a synthesized voice of the robot in this context? To this aim, two versions of the same story for kids from 8 to 9 y.o. have been developed. The social robot Pepper was used to tell the story in two modalities. In the first modality, Pepper storyteller was designed as a kind of audiobook in which the robot had just the role of a device, but the story was narrated by a human voice; in the second modality, Pepper was designed to tell the story using its own voice combined with non-verbal behaviors. The system has been tested in a real context and results show that Pepper’s voice affected more positively the children’s emotional experience, also by giving the children the perception that they learn more easily.