Felix Alexander Sonnenfeld (* March 18, 1910 in Rio de Janeiro  - † February 12, 1993 in Miguel Pereira) was a Brazilian chess composer.

Sonnenfeld began composing chess in 1934. He created 2500 tasks and was known as an auxiliary mat expert. In 1974 he was appointed International Adjudicator of Chess Composition and in 1991 FIDE Master of Chess Composition.

Sonnenfeld was a board member of the Brazilian Chess Federation in 1939, co-founder and president of the União Brasileira de Problemistas for fourteen years in 1960 and a founding member of the Clube des Xadrez Guanabara in 1972. He was the Brazilian delegate of the PCCC until 1991.

Sonnenfeld was the son of German immigrants.