At the end of the 2 1/2-hour hearing, the judge accepted the plea and declared Castro guilty. Sentencing was set for Thursday.
The women said in a statement they were relieved by the conviction.
"They are satisfied by this resolution to the case, and are looking forward to having these legal proceedings draw to a final close in the near future," said the statement released on their behalf.
Gina DeJesus, Amanda Berry and Michelle Knight disappeared separately between 2002 and 2004, when they were 14, 16 and 20 years old. Each said they had accepted a ride from Castro, who remained friends with the family of one of the women and even attended vigils over the years marking her disappearance.
He was accused of repeatedly raping, beating and restraining the women, sometimes chaining them to a pole in a basement, to a bedroom heater or inside a van.
Castro fathered a 6-year-old daughter with Berry, now 27, authorities said. On the day the child was born, Christmas 2006, Castro raped one of the other women, who had helped deliver the baby.
Berry told authorities that she, her child and the other women never saw a doctor during their captivity. Knight, now 32, said her five pregnancies ended after Castro starved and repeatedly punched her.
The women escaped Castro's house May 6 when one of them kicked out part of a door and called to neighbors for help. Castro was arrested within hours and has remained behind bars.
Residents of the street where Castro's boarded up house is surrounded by a tall chain-link security fence welcomed the guilty plea and the news that the house would likely be torn down within a month, possibly for a park.
"It's really horrifying to look at and for my kids to see," said De'Andrea Harris, who lives directly across the street with her two children. She said she had no idea anything was wrong in the house until the women were rescued.