Background The purpose of this study was to investigate the efficacy of gelatin sponge impregnated with ropivacaine on postoperative pain after transforaminal lumbar interbody fusion (TLIF) in patients with lumbar degenerative diseases. Methods We retrospectively reviewed patients who underwent TLIF in our department between August 2018 and January 2020. Patients were divided to ropivacaine group and saline group. A ropivacaine group whom received gelatin sponge impregnated with ropivacaine during operation, and a saline group whom were intraoperatively administered by gelatin sponge impregnated with saline. The two groups were compared in reference to postoperative hospital stay, postoperative complications and visual analog scale (VAS) scores. The consumption of postoperative diclofenac sodium suppository use was also recorded. The Oswestry Disability Index (ODI) scores and Japanese Orthopedic Association (JOA) scores were used for functional evaluation at 1 year postoperatively. Result A total of 127 patients were evaluated in this retrospective study. The mean postoperative hospital stay in the ropivacaine group was significantly lower than saline group. The VAS score was significantly lower in patients receiving gelatin sponge impregnated with ropivacaine as compared with patients in saline group on postoperative day 1, 2, 3 and 4. The number of patients who need the administration of diclofenac sodium suppository and the mean consumption of postoperative diclofenac sodium suppository was significantly lower in the ropivacaine group as compared with saline group. Conclusion The application of gelatin sponge impregnated with ropivacaine around the nerve root in patients undergoing TLIF can effectively control the postoperative pain and reduce postoperative hospital stay.