Sowell, 50, was arraigned by video hookup from jail. He kept his cuffed hands on his lap, occasionally looking at an overhead screen showing the courtroom crowded with TV crews.
Asked by Cuyahoga County Common Pleas Judge Eileen J. Gallagher if he was pleading not guilty by reason of insanity to an 85-count indictment, the soft-spoken Sowell responded, "Yes, your honor."
Sowell was on charges that include murder, rape, assault and corpse abuse. He is accused of murdering 11 women and attack three others who survived. He could get the death penalty if convicted of any of the killings.
Photos: Anthony Sowell's Alleged Victims
The prosecutor asked for $14 million bond $1 million for each victim but the judge ordered him jailed without bond. He has been held in an isolation cell at the county jail.
Sowell's court-appointed defense attorney, Brian McGraw, attended the arraignment but said later he didn't know if he would continue to handle the case and couldn't comment.
Assistant Cuyahoga County Prosecutor Richard Bombik said outside court that the insanity plea wouldn't affect the state's case and said he was confident Sowell would be ruled competent to stand trial.
An insanity defense requires a finding that the person suffers from a severe mental illness and cannot distinguish between right and wrong. "I think he will fail miserably on both accounts," Bombik said.
When his defense team is settled, psychiatric testing is likely. The issue will be handled by the trial judge beginning with a pretrial hearing Monday.
Authorities have said Sowell lured vulnerable women, typically homeless or living alone and with drug or alcohol addictions, to his home and attacked them. Of the 11 alleged victims, all black women, 10 have been identified. The remains of 10 women and a skull were found in his home and buried in the yard.
A search of Sowell's former home on Wednesday turned up no new bodies, the FBI said.
Agents using cadaver dogs spent hours looking inside and outside the East Cleveland house where Sowell lived before going to prison for 15 years for a 1989 attempted rape. They took some items, but FBI spokesman Scott Wilson declined to identify what they were and said there were no plans to resume the search.
The renewed search, Wilson said, was part of a wider FBI investigation into the Sowell case, including previously reported plans to search outside the Cleveland area in states he lived while in the military. Sowell served in the Marines from 1978-85 with assignments at Parris Island, S.C.; Camp Lejeune and Cherry Point, N.C.; Camp Pendleton, Calif.; and Okinawa, Japan.