Mints/X11s are neuronal adaptor proteins that bind to amyloid-β precursor protein (APP). Previous studies suggested that Mint/X11 proteins influence APP cleavage and affect production of pathogenic amyloid-β (Aβ) peptides in Alzheimer's disease; however, the biological significance of Mint/X11 binding to APP and their possible role in Aβ production remain unclear. Here, we crossed conditional and constitutive Mint1, Mint2, and Mint3 knock-out mice with transgenic mouse models of Alzheimer's disease overproducing human Aβ peptides. We show that deletion of all three individual Mint proteins delays the age-dependent production of amyloid plaque numbers and Aβ40 and Aβ42 levels with loss of Mint2 having the largest effect. Acute conditional deletion of all three Mints in cultured neurons suppresses the accumulation of APP C-terminal fragments and the secretion of ectodomain APP by decreasing β-cleavage but does not impair subsequent γ-cleavage. These results suggest that the three Mint/X11 proteins regulate Aβ production by a novel mechanism that may have implications for therapeutic approaches to altering APP cleavage in Alzheimer's disease.