Background: The Medical Outcomes Study Social Support Survey (MOS-SS) is a multidimensional, self-administered instrument used to assess various functional dimensions of social support. Less is known regarding its value for a Chinese population., Objective: The aim of this study was to assess the psychometric properties of the MOS-SS on an adult sample in Taiwan., Methods: A total of 265 adult family caregivers of patients with cancer from four different hospitals in the north, middle, and south regions of Taiwan completed the MOS-SS., Results: In the original five-factor model, unsatisfactory item discriminant validity was found in almost half of the items; the item-own subscale correlation was lower than the item-other subscale correlation. A two-factor model accounting for 68.98% of the variance was found using exploratory factor analysis. The first factor (emotional support) accounted for 62.28% of the total variance, whereas the second factor (tangible support) accounted for 6.7%; the interfactor correlation was .71. The two-factor model seemed to have satisfactory reliability and validity and better discrimination between different subscales than did the original five-factor model., Discussion: Good reliability and validity were demonstrated in the MOS-SS when applied to an adult sample in Taiwan. A two-factor model, instead of a five-factor model as found in the Western countries, was found for this sample. Confirmation of the two-factor model and exploration of the two-factor model in related concepts are suggested for future studies.