The city's Board of Health has approved a limit of 16-ounces on sodas and other sugary beverages served in restaurants, movie theaters, food trucks and ball parks.
Grocery stores are exempt.
The aim is to cut calories and whittle the waistline of the more than 50-percent of New Yorkers considered overweight or obese.
"This the single biggest step any city I think has ever taken to curb obesity," Mayor Michael Bloomberg said.
A typical can of soda is 12 ounces, an amount allowed under the ban.
The typical single-serve bottle of soda is 20 ounces.
"This has nothing to do with banning your ability to buy as much, as many sugary drinks as you want, simply the size of the cup that can be used," Bloomberg explained.
A group against the ban called "New Yorkers For Beverage Choices" is threatening legal action, saying it's not fat that will be lost, it's freedom.
"We do not believe that restricting the size of one product in certain establishments in this city is the comprehensive approach that we need to deal with this issue," says Eliot Hoff.
Many obesity experts say it's an important step that's expected to march across the country.
"Boston has started talking about it, a number of cities in California, a number of cities in the Midwest, so what Mayor Bloomberg has done and the city of New York has done has started the dialogue on a critical issue," says the University of North Carolina's Dr. Barry Popkin.
Despite a likely legal battle, the ban is expected to take effect in March.
The ban will not apply to low-cal fruit juices, diet soft drinks or dairy-based drinks like milkshakes.