Oliveira will still face Justin Gaethje in the main event of UFC 274 on Saturday, but only the latter will be eligible to win the belt. If Oliveira wins, the title will remain vacant.
Oliveira is the first UFC champion to lose their belt on the scales.
The 32-year-old Brazilian has a long history of struggles cutting weight but appeared to put the issue behind him during the run to his first championship.
Oliveira won the lightweight belt, which Khabib Nurmagomedov vacated, after defeating Michael Chandler via second-round TKO in May 2021. He defended his title in December against Dustin Poirier, earning a 10th straight win with a rear-naked choke in the third round.
Meanwhile, Gaethje is set for his second attempt at a full UFC title after falling to Nurmagomedov in October 2020. The former interim titleholder rebounded in November 2021, beating Chandler via unanimous decision in a Fight of the Year contender to earn a shot at Oliveira.
Strawweight champion Rose Namajunas and Carla Esparza both successfully made weight at 115 pounds for their co-main event rematch.