Disadvantages of polyetheretherketone (PEEK) cages are their smooth and hydrophobic surfaces and their lack of osteoconductivity. Titanium (Ti) coated PEEK cage has been innovated to overcome these potential concerns. However, few well-designed studies have investigated the efficacy of Ti-coated PEEK cage on interbody fusion in humans. This study aimed to evaluate the efficacy of Ti coating on bone ongrowth at bone-implant surface by simultaneously comparing Ti-coated and uncoated PEEK cages in the same intervertebral space. This study is a prospective comparative study for the two different cages. Twenty-six subjects who underwent one-level instrumented posterior lumbar interbody fusion (PLIF) were included. Two PEEK cages [a plasma-sprayed Ti-coated (PTC-PEEK) and an uncoated PEEK cage] were inserted in the same intervertebral space. Fusion rates, cage subsidence, and vertebral cancellous condensation (VCC) around the cage, which indicates bone growth on the surface of each cage, were assessed by thin-slice computed tomography (CT) immediately (within 1 week) and at 3 months postoperatively. A functional radiograph was obtained at 3 and 12 months postoperatively. Twenty-three subjects showed solid fusion at 3 months postoperatively (fusion rate, 88%). Cage subsidence was not observed. VCC was often observed around the PTC-PEEK cage as evaluated by completely synchronized CT images between immediately and at 3 months postoperatively. Quantified VCC around the cage was significantly larger in the PTC-PEEK cage than in the uncoated PEEK cage (P = 0.01). The Ti-coated PEEK cage exhibits radiographic signs, suggesting bone ongrowth, as represented by VCC around the cage compared with that around the uncoated PEEK cage. The Ti-coated PEEK cage has the potential to promote solid fusion and to improve clinical outcomes in lumbar interbody fusion surgery. Copyright © 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.