Coordinated behavior patterns are one of the pillars of social interaction. Researchers have recently shown that movement synchrony influences ratings of rapport, and the extent to which groups are judged to be a unit. The current experiments investigated the hypothesis that observers infer a shared psychological state from synchronized movement rhythms, influencing attributions of rapport and entitativity judgments. Movement rhythms of observed individuals are manipulated between participants (Experiment 1) or kept constant while the source of the emerging movement synchrony is manipulated (Experiment 2), and both rapport and perceived entitativity are measured. The findings support the assumption that movement synchrony increases attributed rapport and perceived entitativity. Furthermore, mediational analyses reveal that the effects of movement synchrony on perceived unity are not purely perceptual in nature, but caused by psychological inferences. Observers infer the degree to which individuals are a social unit from their movement rhythms.