The purpose of this study was to determine and test treatment-seeking behavior type and decisional factors of the cancer patients after first detecting symptoms. This study used the methodological triangulation. In the first, treatment-seeking behavior type and decisional factor were described based on qualitative data collected from in-depth interviews with 29 cancer patients. Next, they were tested using quantitative data collected from a structured questionnaire involving 165 cancer patients with statistical method. As a result, treatment-seeking behavior from detecting symptoms to visiting a doctor categorized into immediate visit and delayed visit. The decisional factors on time interval between detecting symptoms and visiting a doctor was influenced by the perceived seriousness of symptoms, the experiences of visiting a doctor previously with similar symptoms, social-group influences on visiting a doctor, barriers to visiting a doctor, and health concerns. There were significant relationship between treatment-seeking time and these factors, however, there was no statistically significant relationship between treatment-seeking time and the demographic characteristics. It is expected that results of this study can be used for nursing education data of cancer patients for early diagnosis after detecting symptoms