Education is a social practice and the ability to interact socially is important to social cognitive learning and social learning. Online education is frequently criticized because it lacks social interaction, a sense of social engagement, and the benefits of learning with others. Social ability with computer-mediated social mechanisms is key to participation and contributions in online learning environments. What is social ability in online education, and can it be measured? The purpose of this study was to explicate and develop an instrument to measure the construct of social ability in online learning. The findings demonstrate construct and predictive validity for a measure of social ability in online learning, indicate that the instrument has power for measuring social ability and underlying factors, and suggests that the instrument may be a valuable tool in technology research for collaborative and networked learning.