Self-management of osteoarthritis (OA) of the knee is important for treating this chronic disease. This study developed and psychometrically tested a new instrument for measuring adult patients’ self-management needs of knee osteoarthritis (SMNKOA). The theoretical framework of self-care guided the development of the 35-item SMNKOA scale. Participants (N = 372) were purposively sampled from orthopedic clinics at medical centers in Taiwan. The content validity index was 0.83. Principal components analysis identified a three-factor solution, accounting for 53.19% of the variance. The divergent validity was −0.67; convergent validity was −0.51. Cronbach’s alpha was .95, Pearson’s correlation coefficient was .88, and the intraclass correlation coefficient was .95. The scale’s reliability and validity supports the SMNKOA, as a tool to measure self-management needs of adults with knee OA. Nurses and other health care providers can use this instrument to evaluate knee OA patients and identify strategies for improving health-related outcomes and patient education.