The university's Board of Governors voted 7-0 Friday to require gun bans on its campuses in Fort Collins and Pueblo.
Guns are already off-limits at K-12 schools in Colorado, the University of Colorado and at virtually all campuses nationwide. But Colorado State University has followed state law that allows people to carry guns, even concealed weapons with the right permit.
Both concealed and unconcealed weapons will now be banned.
Officials said the gun ban will leave Utah campuses as the only ones where concealed weapons are allowed. Utah has a law allowing concealed weapons on state property, and a court has ruled there is no exception for colleges.
Colorado State board members acted Friday after a faculty group at the Fort Collins campus asked for a ban.
"Overwhelmingly the faculty feel our campus will be a safer place" with a concealed weapons ban, said Dan Turk, associate professor of computer information systems.
But many students opposed the ban, and the student government at the Fort Collins campus urged the board not to ban guns.
Senior Brady Allen, who lawfully carries a weapon on campus, told the board that fear of an accidental discharge from a concealed weapon was a silly reason to ban guns.
"You might as well ban everything that has a potential risk - cars, alcohol and sports," said Allen, a 25-year-old history student and a former Marine.
Almost all college campuses nationwide ban concealed weapons. But gun-rights advocates say the bans make students vulnerable to attack. The question took on greater prominence in 2007 after a gunman at Virginia Tech killed 32 people and wounded 23 before killing himself.
Since the Virginia Tech massacre, proposals to repeal campus gun bans have been considered in many states, although none has been repealed.