Abstract Background The objective of this prospective randomized monocentric study is to compare the speed and quality of interbody fusion of implanted porous Al 2 O 3 (aluminium oxide) cages with PEEK (polyetheretherketone) cages in ACDF (anterior cervical discectomy and fusion). Materials and methods A total of 111 patients were enrolled in the study, which was carried out between 2015 and 2021. The 18-month follow-up (FU) was completed in 68 patients with an Al 2 O 3 cage and 35 patients with a PEEK cage in one-level ACDF. Initially, the first evidence (initialization) of fusion was evaluated on computed tomography. Subsequently, interbody fusion was evaluated according to the fusion quality scale, fusion rate and incidence of subsidence. Results Signs of incipient fusion at 3 months were detected in 22% of cases with the Al 2 O 3 cage and 37.1% with the PEEK cage. At 12-month FU, the fusion rate was 88.2% for Al 2 O 3 and 97.1% for PEEK cages, and at the final FU at 18 months, 92.6% and 100%, respectively. The incidence of subsidence was observed to be 11.8% and 22.9% of cases with Al 2 O 3 and PEEK cages, respectively. Conclusions Porous Al 2 O 3 cages demonstrated a lower speed and quality of fusion in comparison with PEEK cages. However, the fusion rate of Al 2 O 3 cages was within the range of published results for various cages. The incidence of subsidence of Al 2 O 3 cages was lower compared to published results. We consider the porous Al 2 O 3 cage as safe for a stand-alone disc replacement in ACDF.