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Abstract Study on the regulation of broad‐spectrum resistance is an active area in plant biology.RESISTANCE TO POWDERY MILDEW 8.1(RPW8.1) is one of a few broad‐spectrum resistance genes triggering the hypersensitive response (HR) to restrict multiple pathogenic infections. To address the question how RPW8.1 signaling is regulated, we performed a genetic screen and tried to identify mutations enhancing RPW8.1‐mediated HR. Here, we provided evidence to connect an annexin protein with RPW8.1‐mediated resistance inArabidopsisagainst powdery mildew. We isolated and characterizedArabidopsis b7‐6mutant. A point mutation inb7‐6at theAt5g12380locus resulted in an amino acid substitution in ANNEXIN 8 (AtANN8). Loss‐of‐function or RNA‐silencing ofAtANN8led to enhanced expression ofRPW8.1, RPW8.1‐dependent necrotic lesions in leaves, and defense against powdery mildew. Conversely, over‐expression ofAtANN8compromised RPW8.1‐mediated disease resistance and cell death. Interestingly, the mutation in AtANN8 enhanced RPW8.1‐triggered H₂O₂. In addition, mutation in AtANN8 led to hypersensitivity to salt stress. Together, our data indicate that AtANN8 is involved in multiple stress signaling pathways and negatively regulates RPW8.1‐mediated resistance against powdery mildew and cell death, thus linking ANNEXIN's function with plant immunity.