The changes of bioactive components and antioxidant activity of quince nectar were determined during 9 months of storage at 5, 20, 30 and 40 °C. The amount of total phenolics, flavonoids and antioxidant activity was significantly declined during storage at all temperatures. Loss of L-ascorbic acid at 5, 20, 30 and 40 °C was 32.08%, 43.69%, 65.21% and 88.82%, respectively. L-ascorbic acid degradation was in accordance with the first-order reaction kinetics, and activation energy was found as 43.65 kJ mol−1. After 9 months of storage, Hydroxymethylfurfural (HMF) contents of quince nectars were 15.01, 16.64, 21.69 and 57.89 mg kg−1 at 5, 20, 30 and 40 °C, respectively. HMF accumulation fitted a zero-order kinetic model, and activation energy was found as 88.30 kJ mol−1. A significant correlation was found among L-ascorbic acid, total phenolics, flavonoids and antioxidant activity.