Viorica Ursuleac (26 March 1894 – 22 October 1985) was a Romanian operatic soprano.

Viorica Ursuleac was born the daughter of a Greek Orthodox archdeacon, in Chernivtsi, which is now in Ukraine. Following training in Vienna, she made her operatic debut in Zagreb (Agram), as Charlotte in Massenet's Werther, in 1922. The soprano then appeared at the Vienna Volksoper (1924–26), Frankfurt Opera (1926–30), Vienna State Opera (1930–35), Berlin State Opera (1935–37), and Bavarian State Opera (1937–44). She married the Austrian conductor Clemens Krauss in Frankfurt during her time there.

She was Richard Strauss's favorite soprano, and he called her "die treueste aller Treuen" ("the most faithful of all the faithful").[this quote needs a citation] She sang in the world premieres of four of his operas: Arabella (1933), Friedenstag (which was dedicated to Ursuleac and Krauss, 1938), Capriccio (1942), and the public dress-rehearsal of Die Liebe der Danae (1944).

She appeared at the Salzburg Festival (1930–34 and 1942–43) and in one season at The Royal Opera Covent Garden (1934) where she sang in the first performances in England of Jaromír Weinberger's Schwanda the Bagpiper and Arabella (her favorite role). She also appeared as Desdemona in Verdi's Otello at the Royal Opera, with Lauritz Melchior in the name part, and Sir Thomas Beecham conducting.

Ursuleac sang at La Scala in Richard Strauss's Die Frau ohne Schatten (as the Empress), and Elektra (as Chrysothemis), Mozart's Così fan tutte, and Wagner's Die Walküre (as Sieglinde). Her only American appearances were at the Teatro Colón in Buenos Aires, as Brangäne in Wagner's Tristan und Isolde, opposite Kirsten Flagstad, in 1948. Also in her repertory were the Countess Almaviva (The Marriage of Figaro), Donna Elvira (Don Giovanni), Leonore (Fidelio), Senta (Der fliegende Holländer, with Hans Hotter), Amelia Grimaldi (Simon Boccanegra), Amelia (Un ballo in maschera), Leonora (La forza del destino), Élisabeth de Valois (Don Carlos), Tosca, Minnie (La fanciulla del West), Turandot (opposite Erna Berger's Liù), Der Rosenkavalier, Ariadne auf Naxos (first as the Composer, then as Ariadne), Die ägyptische Helena, etc.

She was awarded the title of an Austrian Kammersängerin in 1934, a Prussian Kammersängerin in 1935. She gave her farewell in 1953 in Wiesbaden in Der Rosenkavalier. She was appointed professor at the Salzburg Mozarteum in 1964.

Ursuleac's voice was not of great beauty, at least as recorded, but she was reckoned a great musician and actress. In the words of one colleague, the soprano Hildegard Ranczak, "Although she had a lovely, facile top, I was constantly amazed at the two hours' vocalizing she went through before each performance. Hers was, in my opinion, a marvelously constructed, not really natural voice which she used with uncanny intelligence". Ursuleac died at the age of ninety-one in the village of Ehrwald in Tyrol where she had resided since before the death in 1954 of her husband, Clemens Krauss.