Provided is a high-capacity and highly-flexible electrode group for thin batteries, a thin battery including the electrode group, and an electronic device in which the thin battery is incorporated. The electrode group for thin batteries includes: a sheet-like first electrode, a sheet-like second electrode being laminated on each of both surfaces of the first electrode, and an electrolyte layer interposed between the first electrode and the second electrode. The second electrode has a polarity opposite to that of the first electrode. The second electrode has a flexural modulus lower than that of the first electrode. The thin battery includes the electrode group, and a pouch-like housing accommodating the electrode group. The electronic device includes an electronic device main body with flexibility, and the thin battery is incorporated in the electronic device main body.
