Who composed this song, sounds like Mozart or Haydn, but not sure?

Jelena, this is a Christian hymn, "Gloria in excelsis Deo" sometimes shortened to "The Gloria." Its original lyrics are in Latin and it starts with what the angels sang when they told the world Christ was born, Glory to God in the Highest.

The Gloria has been sung to many melodies over many centuries. This one, probably the most well known, is actually an excerpt from a Christmas hymn, "Angels We Have Heard on High," the music from a tradition Christmas carol in France with an arrangement by Edward Shippen Barnes,who studied music in Paris after graduating from Yale. The Gloria is its chorus, separating the verses, with the "O" part of the word Gloria extended through a melodic range.