Approximately 90% of low back pain (LBP) diagnoses are non-specific (NSLBP; i.e. with unknown cause). In NSLBP patients, the hamstrings, iliopsoas, piriformis, and tensor fasciae latae are overactive due to weak hip abductor, extensor, and core muscles. Core stability is essential for proper load balance within the pelvis, spine, and kinetic chain, and core stability exercise (CSE) is an exercise treatment regimen for LBP conditions. We investigated how core stability and hip muscle stretching exercises affected NSLBP patients’ physical function and activity. Patients were randomly allocated to three groups. The Stretch group (n = 24) performed exercises for hip muscle stretching for maximal motion; the Strengthen group (n = 22) performed exercises for hip muscle strengthening while maintaining the maximal isometric contraction. The Sham group (n = 20) received gentle palpation of the skin. Therapy was conducted thrice weekly for 6 weeks. Pain intensity, lower back instability, and hip muscle flexibility were measured to assess physical function. Disability level, balance ability, and quality of life were measured to assess physical activity. Data were collected prior to intervention and at 6-week follow-up. There were significant within-group changes for all measurements (P < 0.05). The Stretch and Strengthen groups had greater improvements in pain intensity, disability level, balance ability, and quality of life than the Sham group. Lower back instability and hip muscle flexibility had the greatest improvement in the Stretch group. In conclusion, CSE and hip muscle stretching are effective at improving physical function and activity in NSLBP patients.