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Learning is blocked when a stimulus is followed by an outcome that is identical to what was expected and thus contains no new information. This classic 'blocking' effect exemplifies that learning is driven by the predictive value of stimuli, which in turn should guide the allocation of attentional resources. Stress is known to be a powerful modulator of learning and memory. However, whether stress may affect attentional processing during predictive learning is largely unknown. Here, we combined electroencephalography and eye-tracking with an experimental stress manipulation and a fear conditioning paradigm designed to probe the blocking effect, to determine if and how stress impacts efficient attentional processing during predictive learning. Participants' explicit ratings indicated, irrespective of stress, a blocking effect. The control group further showed preferential attentional processing of predictive vs. unpredictive stimuli, reflected in differential fixation durations and a differential N2pc. Stress abolished this differentiation and led even to sustained attention, indicated by higher late positive potentials, to stimuli with low predictive value. Moreover, stress resulted in an overall increase in the P3b during the blocking phase, suggesting increased attentional processing, presumably due to impaired access to previously learned associations. Together, our results suggest that while control participants paid particular attention to predictive stimuli and reduced attention to unpredictive stimuli, in line with the classic blocking effect, stress before learning reduced this preferential processing. Thus, the present findings highlight the role of attention allocation for predictive fear learning and suggest that stress may impair efficient information processing against the background of prior experiences., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)