To increase the usability of a new chronic disease self-management system, we conducted a usability study of the system among older adults with chronic diseases (n=33) using a paper prototype based on the think-aloud approach. The metrics used to judge system usability were the task incompletion rate, task completion time, frequency of error, frequency of help, satisfaction, perceived usefulness, and perceived ease of use. We also interviewed the participants to elicit their comments on the system design. The quantitative data were analyzed using descriptive statistics, and the interview data were content analyzed. Overall, the participants were able to carry out the self-management tasks with the current design, but several usability problems were discovered with the system navigation, information search and interpretation, information presentation, and readability. The paper prototype study enabled us to identify these system design weaknesses and to make suitable recommendations for design modifications.