Sanders spoke outdoors at CU-Boulder's Potts Field in front of an estimated crowd of 9,000.
The candidate for the Democratic presidential nomination mentioned the two shootings on college campuses that had occurred Friday as well as last week's attack at a community college in Oregon.
Sanders called for greater mental health measures, universal background checks and the assault weapon ban. In the past, he has occasionally parted from party orthodoxy on gun control.
His topics also included campaign finance reform, income inequality and paid medical leave.