The aim of the study was to assess the effect of time (20–50 min) and temperature (160–220 °C) of roasting on the physicochemical and antioxidant properties of cornelian cherry (Cornus mas L.) stones and to select extraction solvents (water and 50% and 80% methanol) to obtain reliable results. To maintain the highest content of bioactive compounds with a high level of antioxidant properties, roasting at a temperature of 160–180 °C for 30–40 min should be considered optimal. Incorrect selection of roasting parameters (>40 min and >200 °C) causes a significant reduction in the bioactive properties of roasted stones. Regression analysis showed a different nature of changes in the determined features during the roasting process at 160 °C than at other temperatures. The use of methanol, especially at a high concentration (80%), to assess the content of bioactive compounds in roasted cornelian cherry stones provides more reliable results.