The starlet is the daughter of pop star Lionel Richie and the wife of musician Joel Madden.
She and Madden are the parents of a 3-year-old daughter and 1-year-old son.
"Contrary to recent speculation, I am not pregnant," Nicole Richie said in a statement issued to People.com.
"This irresponsible reporting continues to feed an atmosphere of self-doubt and insecurity. To publicly point out a change in anyone's body is mean-spirited and cruel. People's bodies change and change again. This is not newsworthy and is a waste of valuable media space that should be used for more important issues."