Princess Maha Chakri Sirindhorn (Maha Chakkri Sirinthon), born Princess Sirindhorn Debaratanasuda Kitivadhanadulsobhak (; rtgs: Sirinthontheppharattanasuda Kitiwatthanadunlasophak) on 2 April 1955 is the second daughter of King Bhumibol Adulyadej.
Her full ceremonial title is Somdech Phra Debaratanarajasuda Chao Fa Maha Chakri Sirindhorn Rathasimagunakornpiyajat Sayamboromrajakumari, which was bestowed upon her on 5 December 1977. Thais commonly refer to her by reducing such title to “Phra Thep”, meaning “princess angel”. Her title in Thai is the female equivalent of the title held by her brother, Crown Prince Maha Vajiralongkorn. The Thai constitution was altered in 1974 to allow for female succession, thus making her eligible for the throne.
As the eldest female child of the royal family (excluding Ubolratana Rajakanya, who married a foreign commoner), her position is comparable to a princess royal.