Siv Elisabeth Margaretha Wärnfeldt (born 1956) is a Swedish author, opera and concert singer.
Wärnfeldt took a bachelor's degree at Stockholm University in music, art and theatre science in 1979.
For many years her vocal teacher was the Hovsångare (Swedish court singer) Birgit Nilsson.
Wärnfeldt has since sung, among others, the part of Donna Anna in Mozart's Don Giovanni at the Södra Teatern, directed by Johannes Schaaf.
Other notable parts are Anna Bolena in Gaetano Donizetti's Anna Bolena, Contessa in Mozart's The Marriage of Figaro, Rosalinda in Strauss's Die Fledermaus and Leonore in Verdi's Il trovatore.