"You're in a different situation now that a felony has been filed," Los Angeles Superior Court Judge Keith Schwartz scolded Lohan after she entered the plea through her lawyer.
"Everybody else has to follow the law. You're no different than anyone else. So please, don't push your luck."
Saying it appeared Lohan had violated her probation in a 2007 drunken driving case, Mr Schwartz set bail at 40,000 US dollars (£24,800) and warned that if she was accused of breaking the law while free, he would have her held without bail.
Lohan, 24, posted bail and was released about an hour after the hearing. She spoke little during the arraignment, except to acknowledge her name and that she understood the charge and possible consequences.
Lohan could face up to three years in state prison if eventually convicted of stealing the necklace in January from a Venice Beach store.
The Mean Girls star has remained in the spotlight throughout her legal problems. She was met by a swarm of photographers and TV cameras when she arrived at the courthouse in a white dress and sunglasses.
Until now, Lohan has struggled with the terms of her probation in the drunken driving case but has not been charged with other crimes.
The former Disney star has been a courthouse regular since May, when another judge determined she had violated her probation by missing weekly alcohol education classes.
She was sent to jail and rehab after missing a hearing then granted early release from both facilities. Within weeks, however, she failed a drug test and was briefly returned to jail before spending the next three months in rehab.