Anthocyanin represents a group of naturally occurring pigments present in many fruits and some vegetables. In addition to contributing to the hues of blue, purple, or deep red common to several plants, these pigments also have potent antioxidant activity. Blackberry in particular is a rich source of antioxidants, largely attributed to the high anthocyanin content associated primarily with the cyanidin-3-glucosides. Despite the in vitro chemical assays that have shown antioxidant activity, very few studies exist which demonstrate the biological implication of the potent antioxidant activity of blackberry anthocyanins, against free radical-induced cellular damage. The purpose of this study was to examine the protective effect of blackberry anthocyanins against free radical-induced intracellular oxidation and cytotoxicity in multiple cell lines, cultured in vitro. Blackberry crude and enriched extract were evaluated against AAPH initiated-intracellular oxidation and AAPH induced-cytotoxicity in one prostate (LNCaP) and two breast cancer cell lines (MCF-7 and MDA-MB-453). Blackberry anthocyanins effectively suppressed AAPH-initiated intracellular oxidation as monitored using DCFH-DA probe. The extracts also decreased AAPH-induced cytotoxicity as assessed using MTT and CellTiter-Glo assay. This study thus demonstrates the effectiveness of blackberry anthocyanins as a potent source of antioxidants that have the affinity to mitigate free radical induced-oxidative damage in different cell systems.