The mechanisms underlying the association between expressed emotion (EE) and the prognosis in early psychosis are still not well understood. Based on the attributional model, this study investigated the association of criticism and emotional over-involvement (EOI) with symptoms and functioning in At-Risk Mental State (ARMS) and First-Episode Psychosis (FEP) patients, and whether these associations were mediated by relatives’ attributions of control and blame. Forty-four patients (20 ARMS and 24 FEP) and their relatives were included. Findings indicated that relatives’ criticism was associated with positive, negative, and general symptoms. EOI was related with negative and general symptoms. Both indices were related with impaired functioning. Most of the relations between EE indices and illness severity were mediated by relatives’ attributions of blame toward the patient. Relatives’ self-blaming attributions and attributions of control over the disorder by either relatives or patients were not associated with patients’ variables or EE. Findings highlight the importance of family emotional environment in the early stages of psychosis, as well as the mediating role that relatives’ beliefs can exert in those relationships. Family interventions aimed to assist relatives to change attributions that blame patient should be included in clinical protocols in order to prevent the entrenchment of high-EE.