| Jayanta Mongkol | |
|---|---|
| Prince Mahisara Rajaharudaya | |
 | |
| Born | 30 January 1866 Bangkok, Siam |
| Died | 15 April 1907 (aged 41) Bangkok, Siam |
| Spouse |
|
| Issue | 13 sons and daughters |
| House | Jayanta (Chakri dynasty) |
| Father | Mongkut (Rama IV) |
| Mother | Concubine Huang |
| Minister of Royal Treasury | |
| In office 26 August 1896 – 1 June 1906 | |
| Preceded by | Srisiddhi Thongjaya |
| Succeeded by | Koed Bunnag |
| Signature |  |
Jayanta Mongkol, the Prince Mahisara Rajaharudaya (Thai: พระองค์เจ้าไชยันตมงคล กรมหมื่นมหิศรราชหฤทัย; RTGS: Phra-ongchao Chaiyantamongkhon Krommamuen Mahisonratchaharuethai; 30 January 1866 – 15 April 1907) was a son of King Mongkut, Rama IV, and his Royal Consort Huang. He was 13 years younger than his brother, Chulalongkorn, who would become Rama V. The prince was a leading member of the progressive clique known as the "Young Siam", on whom King Chulalongkorn relied for support in his efforts to reform the country. At the king's insistence, the younger members of his family and extended family were all educated in Western ways, sometimes attending schools abroad.