He entered the plea in a Malibu courtroom Friday morning and was ordered into an 18-month drug diversion program.
The Los Angeles County district attorney's office says the case will be dismissed if O'Neal successfully completes the program.
The 67-year-old, Oscar-nominated actor was arrested in September along with his son, Redmond, and was later charged with felony methamphetamine possession. Sheriff's deputies had searched the actor's home while doing a check on Redmond O'Neal, who was on probation for a previous drug conviction.
Ryan O'Neal was nominated for a best actor Academy Award for 1970's "Love Story." Redmond, 23, is his son from a relationship with Farrah Fawcett.
