Blagojevich was joined by the parents of a teenager who died of a heart attack last fall after using ephedra. The diet supplement has been blamed for nearly 120 deaths.
"It's a good first step but it's not enough," Blagojevich said of the signing Sunday.
Ephedra drew national attention after officials investigating the February heat stroke death of Baltimore Orioles pitching prospect Steve Bechler linked it to a diet pill containing ephedrine, ephedra's active ingredient.
The herbal supplement is sometimes marketed as an athletic performance enhancer.
The drive for a ban in Illinois began last September with the death of 16-year-old Sean Riggins of Lincoln, whose father said he was taking the supplement to help make the first-string football team.
"We have to make sure that (young athletes) can no longer go to the store and buy ephedra as easily as they can chewing gum," Blagojevich said. The ban took effect immediately.
Riggins' parents, Debbie and Kevin Riggins, are working with Sen. Dick Durbin, D-Illinois, in seeking a nationwide ban from the Food and Drug Administration.
"With the signing of this bill today, we are the benchmark," Kevin Riggins said.
Earlier this month, nutritional supplement retailer General Nutrition Centers said it would stop selling products containing ephedra. Florida Gov. Jeb Bush signed a law last week banning the sale of all diet supplements to children under 18.
The American Heart Association has urged a ban on ephedra sales, and the NFL, NCAA and International Olympic Committee have banned its use by athletes. The National Football League banned ephedra after the 2001 training camp heat stroke death of Minnesota Vikings offensive tackle Korey Stringer.
State Sen. Barack Obama, D-Chicago, the ban's senate sponsor, thanked the Riggins family for pushing the bill.
"They turned their tragedy - the loss of their son - into legislation that is going to save the lives of many young people and athletes," he said.
By Brandon Loomis