Purpose: The purpose of this study was to describe the lived experience of the patients with cancer participating in a clinical trial for the development of a new drug. Method: This study was based on a phenomenological approach. The eight patients participating in a clinical trial were selected as the participations of this study. The data were obtained through in-depth interviews from the participants and were analyzed using the Giorgi method. Results: Essential experiences of the patients with cancer under a clinical trial consisted of anticipating recovery of physical health and a social role, passing the strict criteria of a clinical trial, diminishing economic burden, satisfaction with special treatment receiving, social contribution, concerns about side effects and withdrawal from the clinical trial, conflicts as a participant, pain, limited administration of other treatments, regret for giving up other treatments, strict compliance with instructions, prevention of side effects and maintaining desirable life-style. Integrated units of meaning of these components were hope, good luck, a sense of satisfaction, fear, distress, and the will of self-control. Conclusion: The most essential meaning of the cancer patients participating in a clinical trial was hope. Hope was found to be a primary factor reinforcing the will of self-management. The results of this study can be of great help to the research nurses to understand the lived experience of the patients with cancer and to plan an effective nursing intervention for the patients.