By analysing newly discovered primary materials, the familial and educational backgrounds, and the appointment as a missionary to Korea of Horace G. Underwood were reexamined. Newly discovered facts are as follows: First, about his biological mother and stepmother. His stepmother also played an important role in the Underwood family after John s left in 1882. Second, about educational background. Admission of Horace to NYU may have been possible due to support from people around him, such as his father, who had a passion in his son’s education, from valuable teaching by his pastor Mabon, and from NYU’s free tuition policy at the time. There are two peoples who were very important to Underwood regarding the Dutch Reformed Theological Seminary, Rev. Mabon and Thomas C. Easton, a pastor of the New Brunswick First Reformed Church. Third, about Underwood’s application for missionary to Korea. This study raises the following five questions. 1) What was the exact date when Underwood first recognized Korea? 2) To which field Underwood had prepared to become a missionary? 3) Did Underwood study medicine for a year? 4) Whether Underwood had been fully informed about the plan for Korea of other denominations? 5) The influence of Rijutei s appeal to the American church. ; open