Police say another 81 people have been wounded in the blast. The fatalities include 15 civilians and five troops. Among the wounded are 14 troops, two police and 65 civilians.
Security officials say the first bomb went off in or near the Jolo Cathedral during Sunday Mass, followed by a second blast outside the compound as government forces were responding to the attack.
Jolo Island has long been troubled by the presence of Abu Sayyaf militants, who are blacklisted by the United States and the Philippines as a terrorist organization because of bombings, kidnappings and beheadings.