Study aim: To compare the effects of core stability exercises with an internal attentional focus, an external attentional focus, and no specific attentional focus on pain, quality of life, and proprioception (specific and nonspecific) in individuals with chronic nonspecific low back pain. Design: The present clinical trial was a randomized, double-blind, parallel-group trial with an active control group. It included three groups and a total sample size of 30 participants, with 10 participants in each group. Simple randomization using the lottery method was employed. Settings and conduct: Study setting: Sports Injury and Corrective Exercise Laboratory, Faculty of Sports and Health Sciences, University of Tehran Following screening and confirmation of eligibility by a spine specialist, pain (VAS), quality of life (SF-36), and specific(target angle reproduction error during lumbar flexion and extension) and nonspecific (Y-Balance Test) proprioception were assessed. Participants were then randomly assigned to three groups. Participants and the assessor were blinded to group allocation, and sessions were scheduled to prevent interaction between groups. Participants/Inclusion and exclusion criteria: Men aged 20–40 years with chronic nonspecific low back pain who met the previously stated inclusion criteria, provided informed consent, and received final approval from a specialist physician to participate in the study. Intervention groups: (1) core stability exercises without emphasis on a specific attentional focus (active control group); (2) core stability exercises with an internal attentional focus (attention to the contracting muscles); and (3) core stability exercises with an external attentional focus (attention to the effects of movement or environmental features). Main outcome variables: Lumbar Proprioception; Pain