Identification of chemopreventive benefits of wheat is considered a highly desirable characteristic that could add value to certain cultivars. Several winter and spring wheat genotypes grown in South Dakota were examined to determine their total phenolic and orthorphenolic compound contents as well as antioxidant activities. Spring wheat genotypes were grown at two locations in 2006 whereas winter wheat genotypes were grown at three and two locations in 2006 and 2007, respectively. Total phenolic content was determined by monitoring absorbance following the reaction with Folin-Ciocalteu phenol reagent. Orthophenolic concentration was determined by monitoring the bathochromatic shifts following reaction with sodium molybdate at 350 nm. Antioxidant activity was determined via the scavenging activity of DPPH. Average total phenolic contents and antioxidant activities in spring wheat lines ranged from 0.78 to 1.53 mg g-1 and 6.10 to 9.24% respectively. The winter wheat lines contained the highest amount of phenolic content ranging from 1.56 to 2.22 mg g-1 , as well as the highest antioxidant activity ranging from 7.59 to 21.50%. Antioxidant activities among many winter wheat genotypes were comparable to the cultivar ‘Madison’, a soft red cultivar known to possess a high level of antioxidant activity. Random effects of genotypes estimated through t-statistics of BLUP showed that the spring wheat cultivar ‘Reeder’ had a significantly higher antioxidant content than the grand mean. Likewise three winter wheat genotypes (SD1W064, SD7380-2, and SD97059-2) had superior levels of antioxidant activity compared to the grand mean. Many spring and winter wheat lines performed around the grand mean for total phenolic and orthophenolic contents.