Blackberry is commonly used both in the fresh and the processing market. In the present study antioxidant capacity, organic acids, phenolic compounds, vitamin C, and sugars content of blackberry cultivars grown in the east of Turkey were determined. Phenolic compounds, organic acids, vitamin C, and sugars were determined by HPLC. Antioxidant capacity was determined by spectrophotometric methods. The cultivar Cherokee had the highest antioxidant capacity (48.900 μmol TE g-1), and the cultivar Jumbo had the lowest antioxidant capacity (30.855 μmol TE g-1). It was determined that the chief phenolic compounds in blackberry cultivars were catechin (ranging from 111.599 to 438.970 mg 100 g-1), followed by ellagic acid (ranging from 10.610 to 51.506 mg 100 g-1). Looking at the content of organic acids, citric acid and malic acid came to the fore, ranging from 3.182 to 7.131 g kg-1 and 1.349 to 2.881 g kg-1, respectively. Fructose content of the studied cultivars was higher than the glucose and sucrose contents. Results indicate that blackberry cultivars with higher antioxidant capacity and biochemical content may be valuable for nutritional breeding efforts.