The objective of the present study is to contribute to intervention methods to promote medical social work services that reduce the caregiving burden for the families of cancer patients. For this purpose, this study investigates the ecological system factors including individual, family, and environmental systems factors which affect the caregiving burden of cancer patients' families from an ecological point of view. The subjects of this study were the families of cancer patients over 20 years of age who assumed the primary responsibility to take care of cancer families in a university hospital. A total of 100 questionnaires were used in the analysis. Collected data were analyzed using SPSS 15.0. Frequency analysis, correlation, T-tests, one-way ANOVA tests, and multiple regression analysis were used to analyze the results. The dependent variable used in the analysis was the caregiving burden and was composed of the four sub-factors of physical, social, emotional, and economic burdens. Independent variables affecting the caregiving burden included individual system factors such as self-efficacy, family system factors such as family cohesion and family adaptability, and environmental system factors such as the social support networks of medical social workers as well as those of the patients' families. The results of the analyses are as follows: First, of all the sociological characteristics, health condition, caregiving time per day, and medical treatment type were important factors that influenced the caregiving burden of cancer patients' families. Also, family cohesion was the only factor that influenced the caregiving burden among the family system factors. In addition, the family's social support was the only factor that influenced the caregiving burden among the environmental system factors. Moreover, health condition, caregiving time per day, and family cohesion were important factors that influenced the physical burden; caregiving time per day and medical treatment type were important factors that influenced the social burden; family cohesion was and important factor that influenced the emotional burden; and medical social worker's social support was an important factor that influenced the economic burden. Furthermore, family adaptability among family system factors, self-efficacy among individual system factor and medical social worker's social support among environmental system factors did not influence the caregiving burden. The conclusion is that we need to consider both the families themselves and their environmental circumstances to improve the caregiving burden of cancer patients' families. In particular, an approach which emphasized the health condition, caregiving time per day, medical treatment type, family cohesion, and the social support networks of both the cancer patients' families and those of the medical social workers is requested. To achieve this, practical suggestions for medical social work programs that reduce the families' caregiving burden will have to be developed and prepared.