Background: The prevalence of knee osteoarthritis is increasing due to population aging and an increase in obesity. Besides the mechanical stress caused by weight-bearing and age, osteoarthritis is associated with obesity and metabolic syndrome. Aim: We analyzed the association between non-alcoholic fatty liver disease and knee osteoarthritis.Methods: This cross-sectional, retrospective study was conducted among adults aged >50 years that were enrolled from the 5th National Health and Nutrition Survey (2010–2012). After excluding those diagnosed with chronic diseases, liver diseases, and a history of excessive alcohol consumption, 2,193 individuals were included. A hepatic steatosis index >36 and <30 was considered to indicate the presence and absence of non-alcoholic fatty liver disease, respectively. Knee osteoarthritis was diagnosed according to the Kellgren–Lawrence grade based on knee radiography findings. Results: The risk of non-alcoholic fatty liver disease was 3.653 times higher in the mild osteoarthritis group than in the normal group, and 11.969 and 6.331 times higher in patients with moderate osteoarthritis and severe osteoarthritis, respectively.Conclusions: We found that non-alcoholic fatty liver disease was significantly associated with knee osteoarthritis, and that different odds ratios for non-alcoholic fatty liver disease were observed depending on the severity of the knee osteoarthritis.