Crataegus (Hawthorn) has long been used as a folk medicine and is widely utilized in pharmaceutical preparations mainly because of its neuro- and cardiosedative actions and its low toxicity. The pharmacological effects of Crataegus have mainly been attributed to the polyphenolic contents. In this study, the production of polyphenols by ten-year-old Crataegus monogyna calli was studied in relation to growth variation and antioxidant capacity within a subculture period. Assays based on the Trolox equivalent antioxidant capacity (TEAC( ferric reducing antioxidant power (FRAP) and stability in oil-in-water emulsion were used to characterize the antioxidant actions of the callus cultures. High TEAC (3.66 μmol/g dry weight) and FRAP (208.19 μmol Fe2+/g dry weight) values were observed when maximal growth was reached (days 30–35( and this seemed to be influenced by optimum total phenol (47.40 mg/g dry weight( proanthocyanidin (20.81 mg/g dry weight( flavonoid (7.01 mg/g dry weight( anthocyanin (6.18 mg/g dry weight( (–)-epicatechin (1.77 mg/g dry weight( procyanidin B2 (3.97 mg/g dry weight( and chlorogenic acid (1.11 mg/g dry weight) production during that period. The TEAC values were strongly associated with total flavonoids and to a lesser extent with total phenols, anthocyanins and total proanthocyanidins. The FRAP antioxidant values correlated to total phenols, proanthocyanidins and flavonoids, respectively. The polyphenolic rich calli were as effective as butylated hydroxytoluene (BHT) in preventing hydroperoxide and conjugated diene formation in a 30% oil-in-water emulsion prepared with stripped sunflower oil, during 7 days storage at 30°C. Crataegus monogyna cell culture represents an important alternative source for natural antioxidants.