The 39-year-old actor shared the bad news via Twitter, asking fans to make a donation to the Michael J Fox Foundation which aids Parkinson's disease research, reported Aceshowbiz.
"RIP Pops. James C Reynolds. 1941-2015. If possible, please donate/support," he said.
Jim had been suffering from Parkinson's disease since 1993. Back in 2008, Reynolds wrote a lengthy essay for the Huffington Post about his father's battle with the disease.
"I've watched my father - a strong and proud person who successfully raised 4 arguably insane children - slowly, cruelly stripped of his independence. Witnessing him suffer over the years galvanized my need to step up," he wrote at that time.