She wrote the Comet Song in collaboration with Icelandic author Sjón.
Björk, who is often seen sporting Moomin character T-shirts, says she is a longtime fan of the whimsical creatures.
Moomins and the Comet Chase is to be released in 3-D by the Finnish animation studio Filmkompaniet in the summer of 2010.
The Moomins, who will soon celebrate their 65th birthday, are the brainchild of Finnish author and illustrator Tove Jansson. Her 13 Moomin novels and thousands of Moomin cartoons have been translated into 40 languages.