His comments follow a 19-year-old, who participated in paramilitary drills with a white nationalist group, being charged with murder over the deaths of 17 people who were shot at a Florida high school.
An emotional Kimmel said on his US TV show, Jimmy Kimmel Live!, that it was "another very sad day in America. Another senseless shooting".
After excerpts from the president's speech in the aftermath of the Florida shooting, in which he promised to act on mental health, Kimmel said: "Tell your buddies in Congress... all the family men who care so much about their communities, that what we need are laws. Real laws that do everything possible to keep assault rifles out of the hands of people who are going to shoot our kids," Kimmel said.
"Go on TV and tell them to do that. That is a perfect example of that common sense you told us you were going to bring to the White House."
Kimmel added: "Tell these Congressmen and lobbyists who infest that swamp you said you were going to drain - force these allegedly Christian men and women who stuff their pockets with money from the NRA, year after year after year, to do something. Now. Not later."
While "children are being murdered" the president has "done worse than nothing", he said, adding that "one of your very first acts as president was to roll back the regulations that were designed to keep firearms out of the hands of the mentally ill".
Meanwhile, the FBI has apologised for failing to act on warnings about the Florida school shooting suspect.
They were told by someone close to Nikolas Cruz that he was a "potential threat to life", but it wasn't followed up.
The state's governor has called on its director to resign.
Mr Trump came face-to-face with hospitalised victims from the horrific school shooting in Florida and offered thanks to the doctors and nurses who helped the wounded, declaring "the job they've done is incredible".
Asked if he had talked with victims, Mr Trump added: "I did indeed, and it's very sad something like that could happen."
The president had tweeted earlier that he would meet with people "whose lives have been totally shattered".
Mr Trump and first lady Melania Trump visited Broward Health North Hospital to pay their respects to the medical professionals who had responded to the shooting in nearby Parkland.
But some of the parents, survivors and others affected by the tragedy at Marjory Stoneman Douglas High School were more interested in firm action to prevent future assaults than a presidential visit.
"I don't want Trump to come but we want more gun safety," said 18-year-old Kevin Trejos, a senior at the school where 17 people were killed and 14 injured. "It's a dream. It hasn't hit me yet."
Mr Trump, who frequently boasts about his support for the National Rifle Association, made no mention of gun violence or any new measure to restrict access to firearms during remarks on Thursday about the shooting. He did promise to tackle school safety and "the difficult issue of mental health".
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