"Over 1,057,000 people have been killed by guns in the USA since John Lennon was shot and killed on 8 Dec 1980," Ono, the former Beatle's widow, tweeted.
Below the message she included a photo of what appears to be Lennon's blood-stained eyeglasses, perched on a ledge with the Manhattan skyline as a backdrop.
Lennon was shot and killed outside the Dakota apartment building in Manhattan as he and Ono returned to their home. Ono still lives there.
The bold text above the graphic photo is black, except for the words "Over 1,057,000" and "John Lennon," which appear in bright red.
Ono posted several more messages, including: "The death of a loved one is a hollowing experience. After 33 years our son Sean and I still miss him. Yoko Ono Lennon," and "31,537 people are killed by guns in the USA every year. We are turning this beautiful country into a war zone."
Earlier this week, Ono tweeted filmmaker Michael Moore asking for his support.
"Michael Moore @mmflint Join me to kick off a mass movement against gun violence from your living room on Sat March 23 - Yes! love, yoko".
In other Twitter messages Ono, 80, linked an Oxfam video about global arms and the ammunition trade, a newspaper article on actors joining the