"Kookaburra Sits in the Old Gum Tree" was written more than 70 years ago by Australian teacher Marion Sinclair for a Girl Guides competition, and the song has been a favorite around campfires from New Zealand to Canada.
The teacher died in 1988, and publishing company Larrikin Music owns the copyright to her song about the native Australian bird. Larrikin filed the copyright lawsuit last year.
"I have come to the view that the flute riff in "Down Under" ... infringes on the copyright of Kookaburra because it replicates in material form a substantial part of Ms. Sinclair's 1935 work," Federal Court Justice Peter Jacobson said.
He ordered the parties back in court Feb. 25 to discuss the compensation Larrikin should receive from songwriters Colin Hay and Ron Strykert and Men at Work's record companies Sony BMG Music Entertainment and EMI Songs Australia.
Adam Simpson, Larrikin Music's lawyer, said outside court the company might seek up to 60 percent of the royalties "Down Under" earned since its release - an amount that could total millions.
The songwriters and their recording companies did not immediately comment.
"Down Under" and the album "Business As Usual" topped the Australian, American and British charts in early 1983. The song remains an unofficial anthem for Australia and was ranked fourth in a 2001 music industry survey of the best Australian songs. Men at Work won the 1983 Grammy Award for Best New Artist.