After spinal fusion surgery, sacroiliac joint (SIJ) pain has lately attracted attention as a cause of low back pain. There are two risk factors for postoperative SIJ pain: lumbosacral fusion and long segment lumbar fusion. lumbosacral fusion has a very significant incidence of SIJ pain in multiple-segment lumbar fusion. Furthermore, the development of SIJ pain in such circumstances may be early. Patients who had multiple-segment lumbar fusion at Sohag and Fayoum Universities between November 2013 and January 2018 were included in the study. The overall number of eligible patients was 191, with 64 developing postoperative low back pain. Seventeen of them reported new-onset SIJ pain. Using Japanese Orthopedic Association (JOA) ratings, we evaluated postoperative SIJ pain development, duration from surgery to SIJ pain beginning, and postoperative treatment results in SIJ pain patients. The incidence of new-onset SIJ pain was correlated with the lumbar fusion group and the lumbosacral fusion group. SIJ pain was substantially more common with lumbosacral fusion group (28.6%) than with lumbar fusion group (4.7%). The lumbar fusion group had a mean time of onset of SIJ pain of 9.43±1.32 (3-16) months after surgery and the lumbosacral fusion group had a mean time of onset of 3.64±2.65 (2-11) months after surgery, demonstrating that incidence occurred substantially sooner in the lumbosacral fusion group. The mean JOA score in the lumbar fusion group increased considerably from 4.45 at the time of onset to 9.87 at the time of final follow-up; however, in the lumbosacral fusion group, it improved from 5.17 at the time of onset to 7.21 at the time of final follow-up, showing no significant improvement. In this study, we Correlate postoperative SIJ pain with two risk factors (long segment lumbar fusion (>2) levels and lumbosacral fusion).