Although the radial nerve palsy associated with fracture of the humerus recovered in eighty to ninety percent, the management of the nerve palsy is controversial up to the present. We preferred to treat it with open reduction of the fracture and early exploration of the radial nerve. Fourty one cases of radial nerve palsy associated with fracture of the humerus shaft were analysed. The following results were obtained. l. Incidence of radial nerve palsy associated with humerus fracture was 41 cases(21.9%) of 187 humeral fractures. The radial nerve was the most vulnerable to injury at the distal one-third of the humerus in 21 cases (51.2%), especially when there were open (two times more than closed fracture) and comminuted fracture in 22 cases (53.7%). 2. Early exploration of the radial nerve was performed in 27 cases, except 14 cases due to local infection, poor general condition and transferred cases from another hospital. This status of radial nerve in operative fields showed contused in 18 cases, stretched in 4 cases, kinked in 3 cases and ruptured in 2 cases. 3. The average duration of initial recovery of radial nerve palsy is 6.5 weeks in contusion, 10.5 weeks in kinking and 13.6 weeks in stretching. The average duration of final recovery is 21.8 weeks in early explorationa and 35.2 weeks in late exploration. 4. Twenty two cases(81.5%) of 27 cases treated with early exploration and 5 cases(35.7%) of 14 cases treated without early exploration showed improvement on electromyographic finding checked 3 months later after injury and the final recovery rate of radial nerve palsy was 88.9% in early exploration and 66.7% in the late exploration.