In amyloid β-related angiitis, cortical or subcortical microbleeding or cortical superficial siderosis supports clinical diagnosis. However, here we present a 75-year-old female case of amyloid β-related angiitis that did not initially show these lesions. The patient developed right homonymous hemianopia and aphasia, and subsequently became comatose. Her brain lesions progressed extensively from the left occipital lobe to the bilateral cerebral hemispheres, with diffused leptomeningeal lesions and scattered DWI high-intensity lesions. After pathological diagnosis, steroid treatment improved her symptoms as well as imaging findings. No hemorrhagic lesions were detected in the T2*-weighted imaging performed before treatment. However, susceptibility-weighted imaging performed after treatment showed a number of lesions with microbleeding. The clinical features of amyloid β-related angiitis that do not show hemorrhagic lesions at onset should be investigated for rapid therapeutic intervention in the future.