Background: Sacroiliac joint (SIJ) pain after spinal surgery is a common problem. The aim of this study is to report the frequency of new-onset SIJ pain after spinal fusion surgery and to evaluate the response to intra-articular SIJ injection. Subjects and methods: This is a prospective study including a total of 41 patients who had lumbar or lumbosacral fixation and fusion from June 2017 to December 2018 and developed postoperative SIJ pain that was not responding to conservative treatment and therefore underwent intra-articular SIJ injection. These patients were followed up for six months after injection. Patients were assessed with the visual analogue scale (VAS), the Oswestry Disability Index (ODI) and Odom’s criteria. Results: The mean age was 46.29 ±11.08 years and males presented 53.7%. Thirty-three patients (80.5%) had positive provocative tests and 27 patients (65.9%) had severe pre-injection pain with equal pre-injection VAS and ODI scores. There was a significant improvement in post-injection VAS and ODI scores (p<0.001). Excellent Odom’s criteria were achieved in younger patients (p= 0.039), and in patients with moderate pre-injection VAS/ODI scores (p<0.001). Thirty-two patients (78%) had a satisfactory response after three months. Conclusions: SIJ pain is common following spinal fusion surgery. Good to excellent improvement of disability and pain could be achieved within 3-6 months after intra-articular injection. SIJ Injection could be an effective option to improve the outcomes in patients who failed conservative medical management.