Circulating relaxin (RLX) is altered in patients with diabetes mellitus (DM) or cardiovascular diseases. This study was designed to evaluate the changes of RLX in patients with unstable angina (UA) complicated with various categories of abnormal glucose metabolism. Patients who confirmed UA by angiographic and clinical standard were grouped according to the glucose metabolism status with oral glucose tolerance test (OGTT) and medical history categorized as normal, prediabetes, newly diagnosed type 2 DM (T2DM), and previously diagnosed T2DM. Serum RLX-2 was measured and islet beta-cell function was evaluated. The severity of the coronary arterial lesions was evaluated with Syntax Scores. Serum RLX-2 was significantly higher in UA patients with prediabetes (median [quartiles]: 9.87 [7.48, 32.58] pg/mL) and newly diagnosed T2DM (18.36 [9.52, 48.08] pg/mL), compared with those with normal glucose tolerance (6.24 [4.02, 7.27] pg/mL, both P < 0.05). Interestingly, UA patients with previously diagnosed T2DM exhibited lower RLX-2 levels (4.17 [3.23, 5.72] pg/mL) compared with those with normal glucose tolerance (P < 0.05). Subsequent analyses indicated that serum RLX-2 was positively associated with parameters of islet beta-cell function, C-peptide, and fasting insulin levels; however, it was negatively associated with the levels of fasting glucose, 2-hour postprandial blood glucose, HbA1c, and insulin sensitivity, suggesting a potential protective role of RLX-2 during abnormal glucose metabolism in UA patients. Serum RLX-2 was not correlated with the Syntax Scores in these patients. Serum RLX-2 is a potential marker for UA patients with early glucose metabolism abnormality, and increased RLX-2 level was correlated with preserved islet beta-cell function.