Objectives: This study examines the post-traumatic growth (PTG) of bereaved families who care for cancer patients and related factors in Japan. Methods: Participants included 1298 members of bereaved families of cancer patients (aged 20 or older). An anonymous self-administered questionnaire on PTG, coping, and social support was mailed to 496 bereaved families who provided written informed consent. Results: Responses were obtained from 476 bereaved families; however, since 28 families had missing data, 448 were included for the analyses. The mean age of participants was 61.4 years: 69% women and 45% spouses. The average age of the deceased was 72.8 years old for men (59%). The PTG score of the bereaved families was higher for women than for men (p < 0.0001). Moreover, the Post-Traumatic Growth Inventory Score for those above 65 years of age was higher than of those below 65 years of age (p < 0.0001). A regression analysis confirmed that emotion-focused coping, problem-focused coping, relationship with the deceased, advanced age of bereaved families, and emotional support impacted PTG. Conclusion: The significance of the deceased for the bereaved, bereaved family members being older in age, emotion-focused coping, problem-focused coping, and emotional support suggest that these aspects are associated with psychological growth in terms of accepting the death of a loved one and moving forward. It is necessary to evaluate the relationship between the bereaved family and the deceased, the age and gender of the bereaved, coping behaviors, and support status and establish a higher quality bereaved family care system.