Abstract This study examines associations between brain levels of amyloid-β and tau with representational pattern similarity in amygdalar reactivity to negative and neutral images in older adults without dementia. 81 participants viewed affective images during functional magnetic resonance imaging (fMRI). Participants rated the images on valence and arousal outside the scanner. Amyloid-β and tau were measured with 11 C-Pittsburgh compound B and 18 F-MK-6240 positron emission tomography (PET) imaging. Representational pattern similarity analyses compared amygdalar responses to negative and neutral stimuli, while preserving the voxel-wise pattern of fMRI activation. Greater differentiation in the pattern of responding across the amygdala was indicated by lower similarity between negative and neutral stimuli. Greater tau levels in the entorhinal cortex and amygdalae were associated with less pattern similarity in left amygdalar reactivity to negative and neutral images in participants whose tau level was below standard positivity thresholds. Less pattern similarity in right amygdalar reactivity to negative and neutral images was also associated with the participants’ valence and arousal ratings of the stimuli. No associations were found with global amyloid levels and only the association between entorhinal tau and amygdalar similarity remained significant after Bonferroni correction. Greater amygdalar pattern separation in response to negative and neutral stimuli with higher levels of entorhinal tau suggest greater amygdalar sensitivity to negative compared to neutral information as tau accumulates in the brain, suggesting a potential underlying mechanism for the disrupted emotional processes often observed in preclinical Alzheimer’s Disease and other Related Dementias.