The purpose of this study was to determine the effectiveness of using a mobile socially assistive robot (SAR) that incorporates approach behaviour (APB) for seniors. The participants were 15 residents in a nursing home. The effectiveness of dialogue with participants was compared for two types of SARs: stationary and mobile. Interactions were also examined to determine the factors that led to the success or failure of the dialogue based on the trajectory of the mobile SARs and observations of the participants’ behaviour with the mobile SARs. The results showed that nine of 15 participants (60 %) engaged in dialogue with mobile SARs, which was twice as effective as stationary SARs. Conversely, some participants could not engage in dialogue when using a mobile SAR. In addition, these participants’ The Mini-Mental State Examination (MMSE) scores were low. These participants’ successful dialogues were influenced by the angle at which the mobile SAR approached the participant and the length of time the mobile SAR and the participant were face to face. In this study, it was shown that the introduction of mobile SARs in a nursing home could facilitate communication between SARs and residents and further contribute to the quality of life of residents.