The phase I trial is the first step in administering a drug to humans, but it has no therapeutic purpose. Under the absence of therapeutic purpose, healthy volunteers demonstrated different motivations, unlike the actual patients participating in trials. There were many reported motivations, such as financial motivation, contributing to the health science, accessing ancillary health care benefits, scientific interest or interest in the goals of the study, meeting people, and general curiosity. The aim of this study was to identify the motivation and characteristics of healthy volunteers participating in phase I trials in the Republic of Korea. We gave surveys to 121 healthy volunteers to study their demographic characteristics and the reasons of participation. We identified whether the decision to participate in the research was influenced by demographic factors and whether the perception and attitudes toward the research were influenced by the characteristics of the healthy volunteers. After completion of the first survey, 12 healthy volunteers who had participated in a phase I clinical trial were selected to answer the second interview. According to our survey, most healthy volunteers were unmarried men and economically dependent. Most of them participated in the study because of financial reward. The most important factor to measure financial reward was the research period. Also, 43% of the volunteers were university students, 42% answered "university graduation" and 55% were residing in family-owned houses. Many healthy volunteers were found to be living in family homes and to have a student status or lack of economic independence. Results of the survey showed that 64% of respondents indicated having more than one clinical trial participation. In-depth interviews showed that healthy volunteers had diverse motivation to participate in research and that healthy volunteer perceive the clinical trial positively. The main motivation for healthy volunteers' participation in research was "financial reward." Healthy volunteers also considered research schedules, processes, and safety, and had a positive perception of clinical trials, but they thought that the public has a negative perception.