The 6-foot-9, 265-pound big man told ESPN.com that he committed to Mike Krzyzewski and the Blue Devils on Monday night. The Nigerian native averaged 11.4 points and led Conference USA in rebounding (9.3) as a freshman this past season.
He also considered Michigan and Vanderbilt.
Duke will bring in the top-ranked player in the country next season, 6-foot-11 Jahlil Okafor, but it's likely that he only stays in Durham for one season.
Obi will sit out next season and have three years remaining at Duke.
Obi decided to transfer from Rice after the school fired Ben Braun last month.