One element of the law allowed court approval instead of parental consent, but a lower court ruled that was unworkable.
The appeals court disagreed.
For years, anti-abortion groups have said the law should be enforced.
"I'm sure we'll se a decrease in the number of abortions among teenagers because involving parents in their children's decision is always a good thing," Ann Scheidler, of the Pro Life Action League, said.
Planned Parenthood of Illinois issued a statement saying:
"The court made an unfortunate ruling. In some cases, safe and open communication is not possible. In those cases, research shows mandatory parental notice laws do not enhance patent-teen communication but they may be harmful to teens' health and well being."
The law could take effect within weeks.
