Carl Gustaf Ottelin (1 May 1793 – 18 October 1864) was a Finnish prelate who was Bishop of Porvoo from 1838 till 1864.

In 1816, he published De Fide religiosa, a book intended for the Docent, which was rejected by Anders Johan Lagus.

Ottelin served as a lecturer at the Porvoo High School from 1816 to 1831 and taught Russian and mathematics.

After becoming the vicar of Vyborg, he was appointed by Tsar Nicholas I as Bishop of Porvoo on 28 March 1838.

He was consecrated in June of the same year by Archbishop Erik Gabriel Melartin in Turku Cathedral.