"[Ryan is] a great Republican. He's one of the brightest stars in our party," Priebus said on CBS's "Face the Nation."
"He's a great friend. Smart. One of the most pure-hearted people I've ever known in politics."
Priebus's comments come after reports surfaced earlier this month that Ryan would no longer defend or campaign for Trump.
Ryan's decision came after the release of a 2005 video in which Trump talked about how he could grope and kiss women without their consent because of his celebrity status.
Trump has since attacked Ryan, saying the Speaker is a man who "doesn't know how to win" and should be focusing on the issues facing this country instead of fighting the GOP nominee.
Priebus on Sunday also said all Republicans should support the nominee of their party.
"I think ... when you have two parties, this isn't Italy, we don't have 12 different parties where everyone can fit neatly into a box," Priebus said.
"And so you have to understand that. Our job is to bring as many people into the room as possible and make the case. And so that's what we're doing every day."
Priebus also noted he expects Trump will do better in black communities than the GOP has done in past elections.
"We are the party of Lincoln," Priebus said.
"We are the party of equality, freedom and opportunity, and that's what we'll always be."