The literature on heritage speakers’ grammatical processing abilities is still mixed but suggests that comprehension and production abilities differ from native speakers’, and proposes that heritage grammar might bear similarities with second language processing (i.e., Montrul, 2010; Polinsky 2011). The aim of this study was to investigate clitic pronoun processing in heritage speakers of Spanish who did not receive formal literacy in Spanish. Spanish clitic pronouns are complex structures that have been shown to be processed differently in heritage speakers, especially when literacy in lacking in the heritage language (Kato et al., 2009). Critically, clitics agree with the antecedent both in grammatical gender and number, and they undergo syntactic movement, making them fragile for heritage speakers. In this study, we tested 60 heritage speakers of Spanish (age: 19-25) using EEG while they processed sentences containing clitic pronouns. We hypothesized that if heritage speakers are sensitive to the violations of grammatical gender and/or number (probed by the experimental manipulation) the emergence of a P600 when presented with clitic pronoun violations should be observed. In addition, participants also completed a behavioral battery including a language history questionnaire, a Spanish grammar task, and a memory task (O-Span). Overall, there was no sensitivity to clitic pronouns violation. However, three major patterns emerged. For some participants, a P600 to gender and number violation was observed, suggesting more native-like sensitivity. Instead, for another subset of participants, an N400 component emerged, in line with previous work suggesting that processing through semantics. Overall, this data points towards a variable neural response in syntactic processing in heritage speakers. Data will be discussed under current neurobiological models of syntactic processing, and emphasis will be placed on the role of literacy as a variable to provide syntactic input.