The bequest calls for $200,000 to be used for financial aid at the all-boys school and $300,000 to be used for expansion of the campus, school officials said.
The Rev. John B. Flanagan, president and rector of the school, hailed Maksin's donation.
"This gift will help immediately," Flanagan said. "Through his generosity, we can help students right now.
"Part of what is so amazing about his gift is that it indicates the kind of person Joe Maksin was," Flanagan said. "He stipulated that $200,000 would go to poor and needy students."
Maksin was the founder of Maksin Management Corp. in Pennsauken, which provides insurance to high school and collegiate athletic programs across the United States.
Denise LePera, the school's executive director for institutional advancement, said more than half of the students receive some financial assistance. Tuition is $6,750 per year.
Eleven percent of the students' families "are classified to have a negative adjusted gross income upon completion of standardized financial aid forms," LePera said. "Thankfully, Joe's vision and generosity will further benefit these families with additional, vital assistance."
LePera said $300,000 would be used "to create spaces with cutting-edge technology in classrooms and science labs, fine arts facilities second to none, and to always create a challenging academic curriculum" and competitive athletic programs.
Steven Ziegler, a spokesman for the school founded by businessman Thomas E. Cahill in 1890, said Roman Catholic has 1,060 students and is the oldest Catholic diocesan school in the United States.
Maksin had been a "a very active alum," LePera said. "In fact, his giving was substantial" while he was alive.
"In this day and age, here at Roman and every school where you have to pay tuition, students need tuition assistance," Flanagan said.
Joseph Maksin Jr. walked around the school Friday and looked at photos and memorabilia from the last two centuries. "It's amazing," he said.
"Roman Catholic was one of the most important parts of my father's life," Maksin said, adding that his family's home was painted purple inside and out. The school's colors are purple and gold.
"As I was growing up, purple was the dominant color," Maksin Jr. said.
Contact staff writer Vernon Clark at 215-854-5717 or firstname.lastname@example.org.