Since the first case was diagnosed on May 20, 2015, there were 186 confirmed cases of Middle East Respiratory Syndrome (MERS) until the end of outbreak in South Korea. Although medical institutions were the most identifiable sources of MERS transmission in South Korea, similar to other countries, in-depth epidemiological investigation was required for some confirmed cases with indefinite contact history or hospital visit records. The subject of epidemiological investigation in the present study was a 35 year-old male patient diagnosed with MERS (#119) who lived in Asan-city and worked in Pyeongtaek-city. Various potential sources of transmission were carefully investigated. While he could have been exposed to MERS through a friend from Saudi Arabia or confirmed MERS cases in his workplace, neighboring areas, and medical institutions, as well as contacts in his home, the chances of transmission were low; however, the potential for transmission through his local community could not be excluded. Practically, it was difficult to determine the modes of transmission for all outbreak cases in communicable disease that occurred in this short period of time. The investigation to identify the mode of transmission in this case was ultimately unsuccessful. However, the various data collected and analyzed to reveal modes of transmission provided detailed information that could not be collected using only interview surveys.