There is a monument at the entrance of Gasil Catholic Church in Waegwan, Gyungsangbuk-do Province. Its name is the monument for paying tribute to Sung Soon-gyo and his family. According to it, Sung Soon-gyo believed in Roman Catholicism and died a martyr around 1860 AD. The monument was built in 1995, and since then has been an object of respect among the believers in Catholicism. But recently some disputes have arisen concerning the genuineness of the martyrdom of Sung Soon-gyo. What is more, it is in doubt whether he was a real believer in Catholicism. This article was made out to inquire into the true state of things. The conclusions through a close inspection are as follows;1. The documents proving his martyrdom are insufficient and doubtful. 2. His descendents’ testimonies are the only evidence to assert his martyrdom, but to our pity, they are out of all reason. So we cannot trust on them. 3. According to the testimonies, he was said to have been executed by the police around 1860. But his family’s genealogical record shows clearly that he died in Febuary, 1858, which was two years sooner. This is the strong counterevidence to the testimonies. 4. The testimonies are maintaining that in the year 1860 when there broke out the religious oppression called as Gyung-sin persecution, the police arrested him at a village in Sangju and killed him on the spot. But at that time, no execution like that happened throughout the country. 5. It is possible that the testimonies were made up by his descendents hearing the news that so many Christians were arbitrarily executed by the police through Byung-in persecution which took place from 1866 to 1871. But it was a sheer fabrication based on the wrong information. This case is an alarm to the historians that they should pay much attention to the truthfulness in dealing with the testimonies as historical materials. And the Catholic church also needs to be more prudent in designating someone as a martyr. Falsehood reveals itself some day.