Humeral lateral epicondylitis or tennis elbow is a common painful elbow disorder. The cause of tennis elbow is the chronic overload of bone-tendon junction. High prevalence of tennis elbow has a direct impact on the workplace productivity and quality of life. Steroid injection is the very few methods proved to have short-term efficacy in tennis elbow treatment, but it has potential adverse effects like tendon rupture. Temporary paralysis of muscle after botulinum toxin injection may reduce the physical demands and facilitate the normal repair mechanism during recovery. Preliminary studies suggested that botulinum toxin injection is effective in treating tennis elbow. The objective of this study is to compare the effects of botulinum toxin injection with corticosteroid injection in tennis elbow treatment.