Objective To investigate the effect of the sagittal alignment of the spine and pelvis after surgical posterior intervertebral fusion combined with pedicle screw fixation for low-grade isthmic lumbar spondylolisthesis, and to assess the effectiveness. Methods Between October 2009 and October 2011, 30 patients with low-grade isthmic spondylolisthesis underwent surgical posterior intervertebral fusion combined with pedicle screw fixation, and the clinical data were retrospectively reviewed. There were 14 males and 16 females with an average age of 56.7 years (range, 48-67 years). The pre- and post-operative radiographic parameters, such as percentage of slipping (PS), intervertebral space height, angle of slip (AS), thoracic kyphosis (TK), thoracolumbar junction angle (TLJ), sagittal vertical axis (SVA), lumbar lordosis (LL), spino-sacral angle (SSA), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI) were measured. The functional evaluation was made using the Oswestry Disability Index (ODI). Pearson correlation were used to investigate the association between all parameters and ODI score. Results PS, intervertebral space height, AS, and ODI were improved significantly compared with properative ones (P lt; 0.05). Significant differences were found in the other parameters between pre- and post-operation (P lt; 0.05) except TLJ and TK. The alteration of SVA showed significant correlation with the changes of PS, PI, PT, LL, SS, AS, SSA, and ODI. The alteration of SSA showed significant correlation with the changes of PS, PI, LL, SS, AS, PT, and ODI. Conclusion Surgical posterior intervertebral fusion combined with pedicle screw fixation for low-grade isthmic spondylolisthesis can effectively improve and maintain the spinal sagittal parameters. SVA and SSA are adequate to evaluate pre-and post-operative balance. The good clinical outcome is closely related with the improved of SVA and SSA.