Purpose: This study aims to understand the worries that patients and families with a history of colorectal cancer experience. Methods: From January 2011 through January 2013, in-depth interviews and observations were conducted on 3 colorectal patients and 8 family members with a family history of colorectal cancer. The data were analyzed using a micro-ethnographic research method. Results: After colorectal cancer patients and families realized and concerned with their increased chance of getting cancer, Eventually this worry became a motivator causing them to adhere to cancer preventive behavior. Three types of cancer worries were identified: confrontation, uneasiness, and warning. Depending on the type of cancer risk, psychological responses and cancer preventive behavior were found to be varied according on the three types of cancer worries. Patients and families tried to change dietary habits and regulary exercise. To help ease their cancer worries, they started to search for information on colon cancers and attempted to follow recommendations. However, they found that neither detailed guidelines nor systematic management from health professionals existed for families with colon cancer patients. Conclusion: A cancer prevention nursing program needs to be developed based on the level of cancer risk and perceived cancer worries of clients.