A quantitative structureeactivity relationship analysis of the 2-methylquinazolin-4-one and quinazolin-4-imine derivatives, well-known antifolate thymidylate synthase (TYMS) inhibitors, has been performedin the range IC50¼0.4÷380000.0 nmoL/L using the GUSAR 2013 program. Based on the MNA and QNAdescriptors using the self-consistent regression, 6 statistically significant consensus models for predictingthe IC50numerical values have been constructed. These models demonstrate high and moderate prog-nostic accuracies for the training and external validation test sets, respectively. The molecular fragmentsof TYMS inhibitors regulating their antitumor activity are identified. The obtained data open opportu-nities for developing novel promising inhibitors of TYMS.