Abstract Background: Myofascial pain syndrome (MPS) is a very common disorder affecting many muscles such as quadratus lumborum (QL) muscle which finally results in low back pain that disturb people lives. Aim of Study: To compare between passive stretching exer-cises and post isometric relaxation (PIR) technique in treatment of QL trigger points in lower back MPS in pain intensity. Patients and Methods: Thirty-two patients from both sexes, with age ranged between 30-45 years, and moderate disability 20%-40% diagnosed by an Orthopedist as chronic myofascial lower back pain participated in this study. They were allocated into two equal groups; group A received passive stretching ex-ercises while group B received PIR technique. In addition, both groups received a combination consisted of traditional modali-ties in the form of infrared and ultrasound. All patients received three sessions per week for 4 consecutive weeks. Pain intensity was evaluated using the visual analogue scale. Results: There were significant differences in group B as compared to group A. Conclusion: The PIR technique and passive stretching ex-ercises are effective in reducing pain intensitywith a greater ef-fect for the PIR techniquefor patients with lower back QL MPS.