The traditional syrup made of Prosopis pods, known as "algarrobina" or "arrope de algarrobo" in the Andean countries, is commonly used in confectionery and local cuisine to prepare sweets and cocktails. The polyphenolic content of four Prosopis pods syrup samples as well as from the phenolic-enriched Amberlite-retained fraction of the syrup, were analyzed using reversed phase high performance liquid chromatography-diode array detector coupled to electrospray ionization mass spectrometry (HPL-DAD-ESI-MS). The main phenolics in the syrups were apigenin-derived C-glycosyl flavonoids, including 6,8-C-pentoside-C-hexoside, 6,8-dihexoside and quercetin glycosides. The sugar derivative 5-hydroxymethyl furfural was present in most of the samples. All syrups were devoid of cytotoxicity towards human lung fibroblasts and human gastric AGS cells, with IC50 values >1000μg/mL. The phenolic constituents of the syrups are C-glycosylflavonoids with known anti-inflammatory, antioxidant and other nutraceutical properties. The phenolic composition of South American algarrobo syrup is presented for the first time. © 2013.