Believability of Intelligent personal assistants (IPA) has proven to be an important building block of successful human-agent interaction. Yet, only a handful of studies have focused on proposing and validating possible approaches to enhance such believability. We hypothesize that IPAs that are capable of handling multimodal interaction, such as facial expression and hand gestures, can appear more believable to human users. This paper illustrates reasons why such interaction can improve believability, in turn enhancing user’s interpersonal rapport with agent. It also discusses design of a study to evaluate believability in human-agent interactions.