Otto Hübertz Mortensen (1907–1986) was a Danish composer and conductor. He also played the organ and piano. For a number of years he worked at the Royal Danish Theatre as a rehearser for the opera, and later worked at Aarhus University.
As a composer, Mortensen composed both vocal works and instrumental music. He is most famous for arranging countless choral works and for writing the melodies for a number of Danish songs, e.g. Septembers himmel, Min skat, Sommervise (Du danske sommer jeg elsker dig…), and the Norwegian Kringsatt av fiender (lyrics by Nordahl Grieg). In the years leading up to his death, he worked on new melodies to a number of psalms, e.g. At sige verden ret farvel.
The melody for the poem by Helge Rode, Du gav os de blomster, som lyste imod os, was selected by the Danish Ministry of Culture in 2006 as one of 12 songs to be a part of the new Canon of Culture (Danish: Kulturministeriets Kulturkanon) in the category musical scores.