The 6-foot-9, 265-pound forward told ESPN.com that he committed to Mike Krzyzewski's Blue Devils.
The Nigerian native averaged 11.4 points and led Conference USA in rebounding (9.3) as a freshman this past season.
Obi reportedly considered Michigan and Vanderbilt. He will sit out next season and have three years remaining at Duke.
Obi made the announcement via Instagram.
"Happy to officially announce that I will be attending Duke university for the rest of my college basketball career," he wrote. "Very thankful for all the support and love from my family and friends all over, and also to every college Coach that have called and been in involved with me through out this process. Duke it is!!"