In recent years, cocoa products have been extensively investigated, due to their high content of biologically active compounds, such as polyphenols and methylxantines, which have been shown to posses beneficial effects on human health, owing to their strong antioxidant activity. The aim of this study was to determine the phenolic and methylxantine composition, as well as the antioxidant activity of different cocoa products. In order to compare the effectiveness of extraction solvent, and to determine the effect of acidic hydrolisis on polyphenol and methylxantine contents, 70% aqueous methanol and water were used for the extraction and the obtained extracts were then hydrolized. The content of total phenols, total flavonoids, total flavan-3-ols and total procyanidins was determined by using spectrophotometric methods, while the composition of individual phenolic compounds and methylxantines was determined by using high performance liquid chromatography (HPLC-PDA). The highest content of total phenols as well as total flavonoids, flavan-3-ols and procyanidins was determined in cocoa liquor and cocoa powder, while in other cocoa products the total content of these phenolic compounds decreased proportionally with the decrease in the amount of cocoa solids. Higher results were obtained when methanol was used for the extraction (instead of water), while the hydrolisis procedure resulted with lower contents of phenolic compounds and methylxantines. The most abundant flavan-3-ols were (−)-epicatechin (EC) and (−)-gallocatechin (GC), whereas gallic acid was the most abundant phenolic acid. Theobromine is the predominant methylxantine in cocoa products. The extracts were screened for their potential antioxidant activities using three different radical scavenging methods: reactions with 1,1-diphenyl-2-picrylhydrazyl radical (DPPH assay), with 2,2`-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical (ABTS assay) and Ferric reducing antioxidant power (FRAP assay).