The extent of indirect decompression after oblique lateral interbody fusion (OLIF) is one of the most important factors in deciding the strategy. To assess the radiographical predictors of the effect of indirect decompression in patients with lumbar degenerative spondylosis by OLIF. Thirty-two consecutive patients who underwent OLIF at 58 lumbar disc levels were enrolled in this study. The radiographic measurements included central disc height (cDH), dorsal disc height (dDH), right/left foraminal height in sagittal plane computed tomography (CT), and cross-sectional dural sac antero-posterior diameter (CDSD) in axial plane CT. All patients were followed up for 1 year after surgery. All CT parameters (cDH, dDH, CDSD, right foraminal height [RFH], and left foraminal height [LFH]) significantly increased after OLIF (P < .0001). The mean raised height difference was 4.3, 3.4, 3.4, and 2.6 mm for cDH, dDH, RFH, and LFH, respectively. The mean CDSD increase was 1.4 mm. The median values of post/pre-operation (change rates) were 1.5 times in cDH, 1.9 times in dDH, and 1.2 times in CDSD, RFH, and LFH. RFH and LFH change rates were related with both cDH and dDH change rates, while the CDSD change rate was only associated with the dDH change rate (P = .0206*) but not with cDH (P = .2061). There was a significant negative relationship between the CDSD change rate and preoperative dDH (P = .0311*, R2 = 0.0817) but not with preoperative cDH (P = .4864). OLIF should be avoided for patients with preserved high dDH.