A state pension board canceled his entire pension after he was convicted in April 2006, and a lower court later upheld the decision.
His attorneys had argued he should only have to forfeit the part of the state pension he earned as secretary of state and later as governor.
The Illinois Appellate Court agreed, ruling he may keep the pension earned earlier while serving as a Kankakee County official, a state lawmaker and lieutenant governor.
"Ryan will still suffer a financial loss in the termination of the pension benefits he earned while serving as the secretary of state and governor," the court said. "Ryan served the State of Illinois for 30 years and will be losing his pension for 12 of those years, presumably the years he received the highest salary."
His lawyer, former Gov. James R. Thompson, estimated that Ryan would get about $65,000 a year. The entire pension would have topped $100,000 a year, Thompson said.
State Attorney General Lisa Madigan's office said it would appeal the ruling.