Introduction: Antioxidants, isolated from different plant parts, are widely used due to their ability to prevent the development of so-called oxidative stress. Sea buckthorn (Hippophae rhamnoides L.) is one of the plants with expected antioxidant properties. Objective: The aim of the study was to evaluate the antioxidant activity of ethanolic, methanolic and acetonic extracts of H. rhamnoides leaves, ripe and unripe fruits obtained by ultrasound-assisted extraction. Methods: To estimate the antioxidant potential of the extracts the DPPH, FRAP, ABTS and Folin-Ciocalteu methods were applied. Moreover, the influence of the extrahent, as well as extraction time, on this activity was evaluated. Results: Sea buckthorn leaf extracts showed higher activity, contrary to the fruit extracts. Moreover, higher activity of ripe fruit extracts compared to unripe material extracts was found. To obtain the highest content of antioxidants in the extracts, ultrasound-assisted extraction for 60 min with methanol should be applied. Conclusions: The presented in vitro results could lead to the conclusion that H. rhamnoides seems to be a valuable source of antioxidants to be applied in various branches of industry.