Hugo Hasslo (16 May 1911 Bohuslän - 20 January 1994 Stockholm) was a Swedish operatic baritone.
Hasslo studied in Stockholm with Hjaldis Ingebjart and Joseph Hislop and made his debut at the Royal Swedish Opera, as Guglielmo in Cosi fan tutte, in 1940, where he remained until 1964, quickly establishing himself as first baritone.
He was particularly admired in the Italian repertory singing roles such as Figaro in Il barbiere di Siviglia, Belcore in L'elisir d'amore, Malatesta in Don Pasquale, the title role in Macbeth and Rigoletto, di Luna in Il trovatore, Riccardo in Un ballo in maschera, Marcello in La boheme, etc. He also sang in Mozart and Wagner operas, and attempted the tenor role of Cavaradossi in Tosca, in 1943.
In Stockholm, he took part in the creation of Natanael Berg's Genoveva, in 1947, and in Kurt Atterberg's Der Sturm, in 1948.
He made guest appearances in Hamburg, the Royal Opera House in London, the Edinburgh Festival, the latter two in 1959.
Hasslo was also much appreciated in concert and often appeared in oratorios.