Thousands of people attended the memorial ceremony at Virginia Tech, for the 32 students and faculty members shot dead a year ago in Blacksburg, Virginia.
The massacre was carried out by South Korean student Cho-Seung Hui, who opened fire on campus before shooting himself.
A moment of silence was observed for the victims followed by a tolling of bells.
It was the worst mass shooting in modern US history.
Cadet Corps guards kept watch next to a ceremonial candle that was lit at midnight to mark the anniversary.
Meanwhile injured Virginia Tech student Kevin Sterne placed flowers on the memorial stones.