End-to-side (ETS) neurorrhaphy is a controversial technique that is used for nerve transfer to achieve functional recovery. The advantage of this technique is the safety of donor nerve function. In this study, patients with extended upper-arm brachial plexus injury and significant hand weakness that did not meet the clinical criteria for end-to-end nerve transfer (Oberlin transfer) were treated by ETS neurorrhaphy to achieve biceps muscle reinnervation. To evaluate the outcome of ETS for biceps muscle reinnervation in brachial plexus injury patients. Thirteen patients with complete upper-arm and incomplete lower-arm brachial plexus injuries were treated by ETS of the motor branch of the biceps muscle to the ulnar or median nerves using the epineurial window technique. Motor recovery was observed in nine of 13 patients. Good results were achieved in six patients who attained biceps motor power ≥ M3. No additional neurological deficits of the ulnar or median nerves were identified after the surgery. End-to-side neurorrhaphy is a viable treatment option for restoration of biceps muscle function if conventional end-to-end nerve transfer cannot be performed.