An exemplary strap for a portable device includes a hollow ring portion, two elastic members, two connecting strings, two blocks, and a strap attachment coupled to the connecting strings. The ring portion includes at least one restraint with a through hole defined therein. The elastic members are fixed within the ring portion. The connecting strings are coupled to the elastic members respectively, pass through the through hole and stretch out of the ring portion. The blocks are positioned respectively at joints of the elastic members and the connecting strings, and restrained within the ring portion by the at least one restraint for preventing the elastic members from being excessively stretched.