The purposes of this study were; 1) to investigate the thoughts of Korean women badminton singles players before and during their games, 2) to extract rational thoughts in order to make them optimally perform by specifically identifying intentional thoughts which appeared in various situations, and 3) to help those who lack specific thoughts and/or have improper thoughts to have rational and appropriate thoughts for the competitions by providing appropriate programs that fit various competition situations. Twelve players were the subjects of this study(two top-elite level, five national level, and five company/university level players). A half-structured interview representing specific game situations was administered individually in order to identify their thoughts during competitions in general and during strokes. The personal interview questionnaire were made from my experiences as a badminton coach for 20 years and with the help of sport psychology consultants. The interview questionnaire included potential occasions that could happen in singles matches. It was divided into three situations, before and during competitions, and during strokes. After the interview, a qualitative research method was utilized to analyze the content of the interview. Results revealed that the thoughts during the competition were various. That is, there were mixed positive and negative thoughts, and there were specific and non-specific thoughts as well. Differences were found between top-elite and elite players and according to game situations. Especially, top-elite players didn`t yield their will regardless of any situation during the game, rather they even enjoyed those situations or had fun in the situations. In addition, they simply focused on each moment of the game and did their best. They hardly show their emotional swings, nor did they reveal their emotions during the game. Also, top-elite players recognized exactly the situation of each stroke when they or the opponent hit the shuttlecock. They said that they sent the shuttlecock in the direction intended and focused on the place where the opponent could send it back. In addition, they showed relatively low mental changes influenced by external moods or game situations.