A one-component magnetic developer for electrophotography comprises single component magnetic toner particles and at least one fine particulate additive selected from hydrophobic silica, hydrophilic silica and alumina, wherein the toner particles have a specific surface area of 1.4 to 2.0 m²/g and a sphericity degree (DS) of 70 to 90% as defined by formula (I) DS = Cc/CT wherein Cc is the outer circumference of a circle having the same area as the projected area of the toner, and CT is the actual outer circumference of the projected plane of the toner. The developer has excellent flowability and can provide a high density image.