The Roman Catholic Diocese of Ajmer (Latin: Aimeren(sis)) is a diocese located in the city of Ajmer in the Ecclesiastical province of Agra in India.
- 1890: Established as Mission “sui iuris” of Rajputana from the Metropolitan Archdiocese of Agra
- 1891: Promoted as Apostolic Vicariate of Rajputana. At this date the district had only one mission station, Jaipur. Besides this, a Catholic priest resided at Ajmer in charge of a small community of Eurasians and Goanese, and there were also stations for troops at Nasirabad, Neemuch, and Mhow, served by three military chaplains. After the carrival of French Capuchins, other stations were established at Ratlam, Thandla, Mariapur, Jhabua, Jhalrapatan, Parbatpura, and Bhawanikhera. The prefects were Father Bertram, 1892-1902, and Father Fortunatus, from 1903.
- May 22, 1913: Promoted as Diocese of Ajmer
- May 13, 1955: Renamed as Diocese of Ajmer–Jaipur
- July 20, 2005: Renamed as Diocese of Ajmer
- Bishops of Ajmer (Roman rite)
- Bishop Ignatius Menezes (November 15, 1978 – present)
- Bishops of Ajmer – Jaipur (Roman Rite)
- Bishops of Ajmer (Roman Rite)
- Bishop Leo D’Mello (April 21, 1949 – May 13, 1955)
- Bishop Guy-Léandre Le Floch, O.F.M. Cap. (June 13, 1939 – August 9, 1946)
- Bishop Mathurin-Pie Le Ruyet, O.F.M. Cap. (June 8, 1931 – July 4, 1938)
- Bishop Fortunat-Henri Caumont, O.F.M. Cap. (May 22, 1913 – April 4, 1930)