4-Hydroxyphenyl substituted thiopyrimidine derivatives have been synthesized with the starting compound 5-benzoyl-6-phenyl-4-(4-hydroxyphenyl)-1,2,3,4-tetrahydro-2-thioxopyrimidine (1). The compounds optimized geometrically with DFT in Gaussian at the B3LYP/6-31G (d, p) level in order to obtain information about the 3D geometries and electronic structures. The structures were characterized on the basis of H-1 NMR, C-13 NMR, FT-IR, and elemental analysis. All compounds tested in vitro in order to assess their antioxidant activity. On the biological properties including of free radical scavenging ability (DPPH center dot), ABTS(center dot+) assay, PhNHNH2 (phenyl hydrazine) induced haemolysis of erythrocytes and metal chelating activities were performed. The results were compared to standard antioxidants, such as alpha-tocopherol and trolox. The conclusion shows that the compounds thioxopyrimidine (1), dihydropyrimido [2,1-b][1,3]thiazin-4(6H)-one (4) and dihydropyrimidin-2(1H)-ylidene) malonate (5) exhibit a stronger antioxidant activity than the other derivatives. (C) 2018 Elsevier B.V. All rights reserved.