A handheld electronic device is provided, which includes a body and a key layout. The body has a base surface. The key layout is disposed on the base surface of the body and includes a plurality of keys. The key layout is a QWERTY key layout and the keys are adapted for users to press with their left or right thumb while holding the body in single hand or both hands. Each key has a curved surface protruded from the base surface and each curved surface has an inflection point. A distance between two inflection points of the curved surfaces of any two adjacent keys is greater than a distance between two figure centers of the orthogonal projections on the base surface of the curved surfaces of the two adjacent keys.