Purpose: The objective of this study was to identify the relationships between family function and successful aging of vulnerable elderly using the circumplex model. Methods: The participants were the elderly (N=401) who were over 65 years old living in H city under the National Livelihood Security Act. Family Adaptability and Cohesion Evaluation Scale III and Successful Aging Instrument were used. Results: The family function perceived by the study subjects was average $43.20{pm}16.62$ out of maximum 100 points. According to the analysis on family types suggested by circumplex model, there were 183 people for balance family (45.6%) and 218 people (54.4%) for extreme family. The total points on successful aging were $1.67{pm}0.37$ out of 3 points. When the difference in points on the Successful Aging instrument were analyzed according to the scores on the Family Adaptability and Cohesion Scale those points of the balanced family were statistically significant (t=2.087, p=.038). Conclusion: In case of the balanced family type, the level of perceiving successful aging was relatively higher. For the improvement of family function, it is advised that the successful aging perception among vulnerable elderly can be uplifted through a program that enables effective communication with other family members.