Insulin resistance and beta-cell dysfunction are manifestations of rheumatoid arthritis (RA). Apolipoprotein C-III (ApoC3) has been associated with such insulin resistance and beta-cell dysfunction in the general population. Our purpose was to study whether ApoC3 is also related to the insulin resistance and beta-cell dysfunction that are present in patients with RA. Three hundred thirty-eight non-diabetic patients with RA who had a glycemia lower than 110 mg/dl were recruited. Insulin, C-peptide, and ApoC3 were assessed. Insulin resistance and beta-cell function were calculated using the Homeostasis Model Assessment (HOMA2) indices. A multivariable regression analysis was performed to study the relationship of ApoC3 with those molecules and indices adjusting for classic factors associated with insulin resistance that included glucocorticoids. ApoC3 was related to significant higher levels of circulating insulin (beta coef. 0.37 95%CI 0.01-0.73 µU/ml, p = 0.044) and C-peptide (beta coef. 0.13 95%CI 0.05-0.22 ng/ml, p = 0.003), and higher insulin resistance -HOMA2-IR- (beta coef. 0.05 95%CI 0.00-0.09, p = 0.041) and beta-cell dysfunction -HOMA2-%B- (beta coef. 2.94 95%CI 0.07-5.80, p = 0.044) indices. This was found after a fully multivariable analysis that included, among others, prednisone intake and the classic factors associated with carbohydrate metabolism such as triglycerides, waist circumference, and obesity. ApoC3, insulin resistance, and beta-cell dysfunction are independently associated in patients RA.