European Portuguese (EP) is a language with variable stress, and the main cues for stress are duration and vowel reduction. Previous behavioral study has reported a stress “deafness” effect in EP when vowel quality cues are unavailable. The present study recorded both event-related potentials (ERPs) and behavioral data to examine the stress processing by native EP speakers in the absence of the vowel quality cues. Our behavioral result was consistent with previous research, showing that when vowel reduction is absent EP (...) speakers demonstrated a stress “deafness” effect similar to that found in speakers of languages with fixed stress or without any lexical stress marking. In the ERP task, both the trochaic and iambic conditions yielded mismatch negativity (MMN) and late negativity, suggesting that EP speakers are able to discriminate the two stress patterns without vowel reduction at the pre-attentive stage. Moreover, the ERP and behavioral data revealed compatible results regarding the pattern of stress bias in EP. In the EPR task, the MMN and late negativity components were more negative and span over a larger temporal window in the iambic condition than in the trochaic condition, indicating a higher sensitivity for the iambic stress pattern. In the behavioral task, EP speakers responded more accurately and more quickly to the iambic stress. These results match recent developmental findings in the acquisition of stress, but speak against the dominant view in EP phonological literature which assumes penultimate stress to be the regular stress pattern. In addition, both the ERP and the behavioral data showed that EP speakers’ stress processing was influenced by their working memory (WM) capacity. The participants with high WM capacity outperformed the participants with limited WM capacity in the iambic condition. In sum, our results broaden the current knowledge on stress processing by EP speakers at both the pre-attentive and attentive levels. (shrink)