Background: Lateral epicondylitis is a work-related musculoskeletal disorder caused by inflammation of the extensor carpi radialis longus and brevis muscles tendons with symptoms of pain in the lateral side of the elbow and decreased range of motion that causes forearm muscle weakness and disability. This study aimed to compare the effectiveness of blood flow restriction (BFR) training with resistance exercise (RE) in increasing grip strength and forearm disability in lateral epicondylitis patients. Methods: This study used the randomized controlled trial design that involved 28 subjects who were divided into intervention and control groups. All subjects received the treatment 3 times per week for 4 weeks, including the standard ultrasound therapy and electro-muscular stimulation interventions for 20 mins with additional treatment of the low-load BFR training for the intervention group and the high-intensity RE for the control group. This study measured grip muscle strength using a handgrip dynamometer, and functional ability was measured using a patient-rated tennis elbow evaluation questionnaire (PrTEEQ) before and after the treatment session. The statistical analyses of paired t-tests and independent t-tests were used in this study. Results: This study found significant differences between pretest and posttest scores in the measurements of forearm muscle strength (change= 20.0~49.0%, p-values <0.001) and PrTEEQ (change= 64.5~70.5%, p-value <0.001) in the intervention and control groups. In addition, the independent t-tests resulted in significant differences in the score changes of forearm muscle strength and PrTEEQ measurement between these groups with p-values <0.001. Conclusion: This study described that BFR training had better effects on grip strength and functional ability than RE in people with lateral epicondylitis.