Group of 2,3-ring-substituted quinazolinone-derived Schiff bases (Q1-Q4) were prepared and examined for cytotoxicity and DNA-protective potential against free radical-induced oxidative damage. The in vitro cytotoxic effect of compounds was assessed in human renal proximal tubular epithelial (TH-1) and hepatocellular carcinoma (HepG2) cells using MTT assay. The radical-scavenging and reducing potency was determined by DPPH and reducing power assay. The DNA-protective potential against oxidants (Fe²⁺, H₂O₂) was screened by DNA topology and Comet assay. Antioxidant mode of action - total antioxidant cell status (TAS) and activity of individual antioxidant enzymes (SOD, CAT, GPx) were screened on TH-1 cells. The results suggested that Q1-Q4 affected TH-1 and HepG2 cell viability in a dose-dependent manner. Derivatives increased TAS, GPx, SOD, and CAT levels in TH-1 cells. Compounds exhibited significant antioxidant properties and high DNA-protective ability. The structure-biological activity relationships analysis revealed the relation between the structure and efficiency of studied compounds. The modification of C-2/N-3 positions of the quinazolinone nucleus, by differently substituted phenyl moieties, seems to be crucial for the DNA-protective potential of these compounds. Quinazolinone derivatives Q1-Q4 can be considered as an effective antioxidants, non-genotoxic and DNA-protective agents with potential medicinal applications.