This study explored low-income older adults' willingness to (i) complete advance directives, legal documents, whereby an individual designates decision-makers in the event that they cannot make their own decisions about end-of-life treatment preferences, and (ii) the role of social support and other predictors that impact their willingness. This study was conducted as part of a larger study exploring behaviours of advance care planning among low-income older adults. Out of a total of 255 participants from the original study, this study included 204 participants who did not complete an advance directive for data analysis. A cross-sectional study using probability random sampling stratified by ethnicity was used. Older adults residing in two supportive housing facilities or who were members of a senior centre in San Diego, California, USA, were interviewed in person between December 2010 and April 2011. Hierarchical logistic regression analysis revealed that the majority of participants (72.1%) were willing to complete advance directives and the factors significantly predicting willingness to complete included self-rated health, attitudes towards advance decision-making and social support. Participants with a poorer health status (OR = 1.43, 95% CI = 1.07-1.90) were more willing to complete advance directives. Conversely, participants with higher positive attitudes (OR = 1.18, 95% CI = 1.00-1.39) and greater social support (OR = 1.07, 95% CI = 1.00-1.15) were also more willing to complete advance directives. The findings suggest the importance of ongoing support from healthcare professionals in end-of-life care planning. Healthcare professionals can be a source of support assisting older adults in planning end-of-life care. Initiating ongoing communication regarding personal value and preference for end-of-life care, providing relevant information and evaluating willingness to complete as well as assisting in the actual completion of advance directives will be necessary.