[Objective] To explore the effect of obesity on posterior lumbar interbody fusion (PLIF) in degenerative lumbar spinal stenosis (DLSS). [Methods] A total of 124 patients with DLSS who underwent PLIF surgery in our hospital from January 2017 to December 2019 were analyzed retrospectively, according to the preoperative BMI, they were divided into two groups, including 42 obese patients (BMI ≥ 28.0 kg/m2) and 82 non-obese patients (BMI < 28kg/m2). 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, postoperative drainage, resumed walking, incision healing time and incidence of incision complications(P < 0.05). All patients were followed up for 16 ~ 25 months, with an average of 19.58 months. The VAS score and ODI index of the two groups were significantly improved 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 rate 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 increased the intraoperative bleeding, the incidence of incision complications and the risk of adjacent vertebral degeneration in DLSS patients treated with PLIF, but did not affect the clinical efficacy.