Terry Hobbs, the stepfather of Stevie Branch, claimed that singer Natalie Maines accused him of being involved in the deaths of his stepson and the two other boys.
Hobbs cited a letter Maines posted on the Dixie Chicks' Web site and remarks she made at a rally in Little Rock in 2007.
Three teenagers who became known to sympathizers as the "West Memphis Three" were convicted in the deaths, but the Dixie Chicks and others claim they are innocent.
U.S. District Judge Brian Miller found Tuesday that Hobbs couldn't establish "actual malice" - that Maines knew the statements she made were false or that she made them with "reckless disregard" of the truth.
