The Catholic Diocese of Caroline Islands (Latin: Diœcesis Carolinensium) is an ecclesiastical territory or diocese of the Catholic Church in the Federated States of Micronesia and in the Republic of Palau.

The Diocese of Caroline Islands is led by a bishop who pastors the mother church, the Cathedral of the Immaculate Heart of Mary.

It became the Apostolic Vicariate (higher missionary stage jurisdiction, entitled to a titular bishop) of Marianne and Caroline Islands on 1 March 1911.

The diocese was split on 23 April 1993 by Pope John Paul II, resulting in the creation of the present-day Diocese of Caroline Islands and the Apostolic Prefecture of the Marshall Islands.

According to 2022 government statistics, 55% of residents were Catholic; 42% of the population were Protestant and 2% belonged to other Christian denominations.