Rosehips are a valuable ingredient in the preparation of functional foods, pharmaceuticals, and nutraceuticals due to the content of functional compounds, including vitamin C, phenolic compounds, minerals, essential fatty acids and carotenoids [3,4]. Rosehip seeds are a waste product in the production of juices and syrups. They contain from 4.9% to 17.82% oil, and due to their desirable composition, they are successfully used in the production of food and cosmetic oils [5]. Twenty-three fatty acids have been identified in cold-pressed rosehip oil with the largest share of the following fatty acids: linoleic (35.9-54.8%), \(\alpha\)-linolenic (16.6-26.5%), oleic (14.7-22.1%). Saturated fatty acids are present in smaller amounts and represented by palmitic (3-5%), stearic (1.5-2.5%), and myristic (!0.5%) fatty acids [5,6]. Rosehip oil also contains phytosterols with a total content of 589.2-648.5 mg/100 g, mainly \(\beta\)-sitosterol (475.3-529.7 mg/100 g), campesterol (19.2-20.5 mg/100 g), stigmasterol (6.0-7.8 mg/100 g), \(\Delta\)5-avenasterol (24.2-37.9 mg/100 g), \(\Delta\)7-avenasterol (3.7-5.6 mg/100 g) [7]. Sea buckthorn (_Hippocampae rhamnoides_) belongs to the olive family (_Elaengaceae_); it is found in Europe, Siberia, the Caucasus, and Asia. Sea buckthorn berries contain many biologically active substances such as vitamin C (87.45-149.37 mg/100 g, even 1004.85 mg/100 g, depending on the variety, place, and growing conditions), polyphenolic compounds--mainly flavonoids (128.66-282.75 mg/100 g), carotenoids (7.94-28.16 mg/100 g to even 106.25-216.04 mg/100 g), phospholipids (123.40-181.16 mg/100 g), phytosterols (7.68-47.84 mg/100 g) and tocopherols (3.35-6.27 mg/100 g) [8]. Sea buckthorn contains 17-20% of oil in fruit, while in seeds, the content is approx. 10%, although in some varieties, it can reach up to 16%. The oil is the most important product currently obtained from sea buckthorn berries, it has the form of a thick, dark brown liquid, strongly coloring the skin, with a characteristic taste and aroma [9,10]. The seed oil contains more unsaturated fatty acids, sterols, vitamins K and E, and fewer carotenoids, tocopherols, and saturated fatty acids than fruit oil. The content of tocopherols in the sea buckthorn oil is 101-1128 mg/100 g of oil, mainly \(\alpha\)-tocopherol, \(\gamma\)- and \(\beta\)-tocopherol. Sea buckthorn oil is a source of carotenoids with a total content of 314-2139 mg/100 g, among which 30% is \(\gamma\)-carotene, 20%--\(\beta\)-carotene, and 30%--lycopene [8]. The number of methods for determining the stability of edible oils and their resistance to oxidation is constantly increasing [11]. Some of the methods available make it possible to determine one or more oxidation reaction products. Color and fat values are widely used to assess the degree of oxidative degradation of fats: peroxide value (PV), which measures the concentration of hydroperoxides; anisidine value (LA), which is used to determine the level of secondary oxidation products, such as unsaturated ketones and aldehydes; acid value (AV), which indicates the content of free fatty acids, Rancimat index determined on the basis of conductometry [12]. These oil stability tests do not provide comprehensive information about the presence of the product in various oxidation states. Therefore, the assessment of oil resistance to oxidation determined by the concentration of peroxides or volatile products can be unclear [5]. Nowadays, there is an urgent need to apply thermoanalytical methods, e.g., differential scanning calorimetry (DSC), for testing the susceptibility of fats to oxidation. There are two basic techniques: isothermal, in which the sample is heated at a constant temperature, and dynamic, with a controlled temperature ramp [13]. In isothermal experiments, as a result of the reaction between unsaturated fatty acids and oxygen, oxidation induction times are recorded.