The article addresses the transformations experienced by the Chilean Popular Socialist Party between 1948 and 1957. In line with some new interpretations, we state that the process of socialist radicalization must be traced back to the 1950s and had its expression in strategic lines, programs and changes in coalitional politics. We consider that this process of radicalization had in its origins a nationalist character and that in its genesis played a fundamental role the adaptation of elements coming from Latin American nationalistic movements and socialist experiences that stressed their nationalistic character.