[Objective] To explore the effect of obesity on posterior lumbar interbody fusion (PLIF) for degenerative lumbar spinal ste- nosis (DLSS) . [Methods] A retrospective study was conducted on a total of 124 patients who underwent PLIF for DLSS in our hospital from January 2017 to December 2019. According to the preoperative BMI, 42 patients who had BMI ≥28.0 kg/m2 were fall into the obese group, while the remained 82 patients who had BMI＜28 kg/m2 were enrolled into the non-obese group. The documents regarding to perioperative period, follow-up and radiographs were compared between the two groups. [Results] All patients had operation completed successfully. The non-obese group was significantly superior to the obese group in terms of operation time, incision length, intraoperative blood loss, postoper- ative drainage, time to resume walking, time to remove stitches and incidence of incision complications (P＜0.05) . All patients were fol- lowed up for 16~25 months, with an average of (19.58±2.71) months. The VAS score and ODI index of the two groups were significantly im- proved over time. However, there was no significant difference in VAS score and ODI index between the two groups at any corresponding time point (P＞0.05) . With respect of imaging, the disc height significantly increased at the last follow-up and 3 months after operation in both groups compared with those before operation (P＜0.05) . At the last follow-up, there was no significant difference in interbody fusion in term of BSF classification between the two groups (P＞0.05) , but the degeneration rate of adjacent vertebrae in the obese group was higher than that in the non-obese group (16.67% vs 4.88%, P＜0.05) . [Conclusion] Obesity increases the intraoperative bleeding, the incidence of incision complications and the risk of adjacent vertebral degeneration in PLIF for DLSS.