"When I think about you I always smile," Seger sings on the track released for free on the rocker's website Wednesday to mark the one year anniversary of Frey's death.
"You were strong/You were sharp/But you had the deepest heart." the 71-year-old sang.
"It's obviously not meant to be a hit," Seger says about the song in an interview with Rolling Stone.
"There's no chorus per se or title section or anything. The idea was just to honor his memory and talk, very specifically, about my impression of him in 1966 when we first met."
A guitarist for The Eagles, Frey died of complications from rheumatoid arthritis, acute ulcerative colitis, and pneumonia.
"I hope 'Glenn Song' doesn't make his wife Cindy cry." Seger continued to Rolling Stone. "But it probably will."