Little is known about how exclusionary immigration laws affect ethnic identity and self-esteem among Latinx middle school students. Arizona’s SB 1070, which required local officers to verify the legal status of detained individuals, garnered national attention for its impact on immigrant and Latinx communities. This study tested a longitudinal parallel multiple mediation model where perceptions of the effects of an exclusionary immigration law (Arizona’s SB 1070) on self-esteem were mediated by dimensions of ethnic identity (ethnic centrality, ethnic private regard, ethnic public regard). Data were collected from a two-wave survey of 891 early adolescents ranging in age from 10 to 14 years (M = 12.09 years; SD = 0.99), a majority (71%) of whom were of Mexican descent. Analyses revealed an indirect effect of T1 perceptions of this law on T2 self-esteem (7 months later), holding T1 measures constant, with T2 ethnic centrality, private regard, and public regard acting as mediators. Perceived effects of this exclusionary law led to increased self-esteem through increased dimensions of ethnic identity. Results reveal how ethnic identity functions as a multidimensional construct in the process through which exclusionary immigration policy may impact the self-esteem of Latinx early adolescents.