Objective To compare the clinical outcomes of posterior lumbar interbody fusion（PLIF） using simple cage alone fusion with pedicle screw fixationand autogenous bone grafting and cage fusion with pedicle screw fixation in adult spondylolisthesis. Methods From March 2003 to March 2004，Twenty-seven patients with lumbar spondylolisthesis were divided in two groups. In group A, 15 patients were treated by PLIF using simple cage alone fusion with pedicle screw fixation, including 4 males and 11 females, aging 53-68 years. Isthmic defectswere located at L4 in 9 cases, at L5 in 6 cases. Four patients were smokers.Thepreoperative mean disc space height was 5.4±2.3 mm, the mean percentage of slip was 36.8％±7.2%. In group B, 12 patients were treated by PLIF using autogenous bone grafting and cage fusion with pedicle screw fixation, including 3 males and 9 females, aging 56 years. Isthmic defects were located at L4 in 8 cases, atL5 in 4 cases. Five patients were smokers. The preoperative mean disc space height was 5.7±2.5 mm, the mean percentage of slip was 37.8%±6.2%. Two groupswere compared in the amount of blood loss, duration of hospitalization, back pain, radiating pain, fusion rate, the intervertebral disc space height, the postoperative degree of slip and the fusion rate. Results All patientswere followed up for 24-38 months. The mean follow-up was 29(24-36) months in group A and26(24-38) months in group B. There were no statistically significant differences infollow-up period, age,sex, the location of isthmic defects, smoking, the preoperative disc space height and the percentage of slip between two groups (Pgt;0.05).There were no statistically significant differences in the amount of blood loss, the duration of hospitalization, the fusion time between two groups(Pgt;0.05). But there were statistically significant differences in the back pain score, the radiating pain score and the fusion rate between two groups(Plt;0.05).Thepo stoperative disc space height and the degree of slip of the last follow-up were5.8±2.2 mm and 25.6％±7.2% in group A, 6.2±2.5 mm and 24.1％±7.4 % ingroupB, showing statistically significant difference (Plt;0.05). Conclusion The PLIF using autogenous bone grafting and cage fusion with pedicle screw fixations ismore beneficial to improving the fusion rate and preventing longterm instabilities than simple cage alone fusion with pedicle screw fixation in adult spondylolisthesis.