The forces announced that the drill involveed Navy, Air Force and Army forces, such as naval warships and aircraft, as well as Army and Marine Corp troops, Yonhap News Agency reported.
The drills have been held twice a year, usually in June and December.
But this year's drills have been pushed back amid an escalating trade row with Japan stemming from differences over wartime forced labour. Japan, which has made territorial claims to Dokdo, has protested the drills.
"In consideration of the drill's significance and size, the military named it the 'East Sea territory defence exercise,' in order to further solidify its determination to defend the country's territories in the East Sea, including Dokdo," a Navy official said.
South Korea launched the Dokdo drills in 1986. Last year, the drills took place for two days in both June and December.
South Korea has maintained effective control of the nation's easternmost islets with a small police detachment since their liberation from Japanese colonial rule in 1945.
Japan has persistently laid claim to Dokdo, drawing strong condemnation from the Seoul government.
Seoul-Tokyo ties recently have plummeted to a fresh low after Japan dropped South Korea from the list of its trusted trading partners earlier this month following the announcement of tighter export curbs on July 4.
In response, South Korea on Thursday announced its decision to terminate the military information-sharing pact with Japan.
( With inputs from IANS )