This paper analyzes social representations and psychosocial factors related to collective action in the context of the massive protest movement of 2019 in Chile. A total of 262 individuals answered a comprehensive online survey that included measures of participation and repertoire of different forms of collective action, identification with protesters as well as with government, agreement with social movement grievances, collective efficacy, perceived emotional synchrony or collective effervescence, self trascendent emotions, beliefs about violence of social movement and police violence, and five open questions on images of demonstrators and police. Participation in October 2019 demonstrations were associated strongly to all previous variables like identification with demonstrators, perceived emotional synchrony in demonstrations, feeling social awe, elevation, moved and joy, disagreement with beliefs justifying police violence and agreement with beliefs on social movement use of violence. High level of psychosocial variables and participation were associated to a set of words elicited by stimuli such as images of police and demonstrators (justice, injustice, inequality, abuses, rights, bravery, dignity, hope, unity) that could be conceived off as positive social representation of demonstrators as just fighters. Low identification and non participation in mass movement was associated to a negative Le Bon style social representation of demonstrators related to chaos and violence.