Background: Partners of cancer patients are the cornerstone of supportive cancer care. They assume different roles and responsibilities that optimally support the patient. Such support is highly demanding, and many partners report (mental) health problems. However, many of them do not use professional supportive care themselves. Offering a Web-based self-help intervention based on Acceptance and Commitment Therapy (ACT) and self-compassion could be an important resource to support this group. This qualitative study aimed to examine user-experiences with a Web-based self-help intervention based on ACT and self-compassion among partners of cancer patients. Methods: Individual in-depth interviews, about partners’ appreciation of the intervention and lessons learned, were conducted with 14 partners of cancer patients who used the Web-based self-help intervention. Interviews were audio-recorded, transcribed verbatim and analyzed by three independent coders both deductively and inductively. Results: In general, partners appreciated the intervention, however, they also expressed ambivalent feelings towards peer support, the content of the feedback of their counselor, and the ‘tunneled’ structure of the intervention. The majority of the partners reported being more self-compassionate accepting that they experienced negative thoughts and feelings, they reported that they learned to increase the distance between their thoughts and themselves, they indicated being more aware of their personal values, and they thought that they were better able to commit to those values. They also reported other (non-specific) helpful processes such as insight and acknowledgement, positivity, the possibility to tell their story, time for themselves, and feeling closer and more connected with their partner (the patient). Conclusions: Partners of cancer patients indicated to appreciate the Web-based self-help intervention based on ACT and self-compassion. They felt that the intervention helped them to cope with negative emotions, thoughts, and one’s suffering; to practice self-kindness; and to clarify values based on difficult recent experiences. In addition, they felt that the intervention supported them to obtain insight and acknowledgement, positivity, to tell their story, make time for themselves, and feeling closer and more connected with the patient. We think that a Web-based psychological intervention based on ACT and self-compassion may be a valuable contribution in supporting partners of cancer patients.