Lawyers for the shamed TV star argued the trial judge had improperly allowed five additional accusers to testify against him.
Dozens of women have accused the 82-year-old, who shot to fame with family comedy The Cosby Show, of sexual assault over several decades.
In April 2018, he became the first celebrity to be tried and convicted in the "#MeToo" era when a jury found him guilty of drugging and sexually assaulting Andrea Constand at his home in 2004.
He was found guilty on three counts of aggravated indecent assault and sentenced to serve three to 10 years in prison.
But his lawyers appealed the conviction earlier this year, arguing that the lower court judge had allowed testimony and evidence which should have been excluded.
They said the accounts from five new women were "strikingly dissimilar" to that of original accuser Ms Constand, thus making their testimony unfair and prejudicial.
However, the judge in Cosby's trial, Steven O'Neill, said the five women’s evidence had shown "chilling similarities" that pointed to a "signature" crime.
The Pennsylvania Superior Court ruled on Tuesday that Mr O'Neill was right to allow their testimony, even if some of those "prior bad acts" took place 22 years before Cosby's assault of Constand.
Cosby has insisted that any sexual encounters he had were consensual.
He and his lawyers have accused many of the complainants of being gold-diggers seeking money or fame.
He told a news outlet in November he expected to serve the maximum 10-year sentence if he lost the appeal, because he would never express remorse to the parole board.
A representative for Cosby did not immediately respond to a request for comment on Tuesday.