The low back pain is a public health problem, affecting the adult population and the young one. It is estimated that 90% of the population will experience at least one episode of lower lumbar pain during their lifetime, half of whom may have a second painful episode during the same year. Frequently, the mechanical cause (the pain is somatic and deep, caused by lesions in the musculoskeletal tendon or ligament, in non-specific degenerative or inflammatory diseases) but also the psychosocial factors are incriminated. In low back pain, ultrasounds were used for the analgesic effect, muscle relaxing and for the hyperemia effect. The paper has as purpose the study of the effects of applying ultrasound in relieving symptoms of the low back pain. The physical therapy had the purpose of relaxing the muscles in the sub-acute phase, stretching the paravertebral muscles, relaxing the pelvis, toning the abdominal muscles, stretching the psoas-iliac and the sciatic muscles. All the patients received pharmacological treatment consisting in non-steroidal, neurotrophic anti-inflammatory medicines. The evaluation of the patients was performed at the beginning and at the end of the treatment after 10 days and at the examination after 3 months. For the two groups (study and control), the assessment was made on the basis of some indices and scales, where statistically significant results were obtained in both groups, especially for the group receiving the ultrasound treatment (the pulsed form to avoid the thermal effect) and kinetotherapy.