Purpose: This paper reports on the design and testing of a new designed forearm orthosis and explores its efficacious in comparison to the standard counterforce orthosis in patients with lateral epicondylitis. Method: Twenty-four patients were enrolled in this assessor-blinded clinical trial and randomly assigned to two parallel treatment groups. The measures of pain and function, the pain threshold and grip strength were compared using patient rated tennis elbow evaluation (PRTEE) form, algometer and dynamometer respectively at baseline and 4 weeks after treatment. Paired and independent t-test statistical methods recruited for within and between groups comparisons respectively. Results: The both orthoses, counterforce and new-designed, significantly relieved pain, and improved function, pain threshold and grip strength of all patients after 4 weeks application. The new-designed orthosis seemed to be more effective than the counterforce orthosis in pain relief, but there was not any significant difference in efficacious of two types of orthoses regarding function. Conclusions: The new-designed orthosis can significantly relieve pain, improve function, increase pain threshold and grip strength after application. This orthosis seemed to be more effective than counterforce orthosis in relieving pain and increasing the pain threshold probably due to the limitation of forearm supination.Implications for RehabilitationSeveral orthoses have been prescribed in the literature to decrease pain and inflammation of the lateral epicondylitis.The new-designed forearm orthosis is composed of wrist and below elbow counterforce straps that are connected by a non flexible middle part.The new-designed orthosis was better than counterforce orthosis in relieving pain and increasing pain threshold.