Nine new thiazachalcone-based drugs, compounds I - 9, were prepared and fully characterized. The configurations of the photochemical -dimerization products 7-9 were rationalized by semi-empirical calculations. Both the experimental data and the theoretical calculations showed that the delta-truxinic acid type dimer is the most stable isomer of all. All compounds were tested for their antibacterial and antifungal activities. The N-alkylated congeners 4-6 showed strong antimicrobial activities against various bacteria and a yeast-like fungus. The MIC and MBC values were as low as 0.1 mu g/ml. All the compounds were active against the Gram-positive bacterium Staphylococcus aureas.