Patients and Methods:prospective randomized comparative clinical study conducted on 42 patientswith grade I and II isthmic or degenerative lumber spondylolisthesis,this study was carried out at the department of neurosurgery, Zagazig University from 1st of September 2021 till 28th February 2022. Complete history taking, general and neurological examination and imaging investigation were done. Pain score scale (VAS) and Oswestry disability index (ODI) pre and post-operative were measured. The two different surgical interventions were compared. Results:the age ranged from 18 to 60 years, 59.52% were females. Low back pain and leg pain were the main complaint. 73.81% of patients had degenerative spondylolisthesis while 26.19% had isthmic. 64.29% was L4-5 listhesis followed by L5/S1 (33.33%). First degree spondylolisthesis accounted 64.29% and second degree in 35.71%. Complete reduction acheived in 61.9% in PLIF group and 38.1% in PLF one. VAS for all patients had significantly decreased from 7.71±0.83 preoperative to 2.35 ± 0.69 postoperative. The mean ODI among our patients had significantly decreased from 13.19 ± 2.51 preoperative to 3.83 ± 0.91 postoperative. Sagittal Vertical Axis (SVA) improved from 39.7±9.2 to 31.8±8.7 in the PLF group (p=0.007) and from 40.1±9.7 to 30.5±9.1 in the PLIF group (p=0.002). Conclusion:better results were achieved of reduction rate in PLIF. Similar results for VAS, ODI and SVA.