Antimicrobial resistance is a never‐ending challenge, which should be considered seriously, especially when using unprescribed “over‐the‐counter” drugs. The synthesis and investigation of novel biologically active substances is among the directions to overcome this problem. Hence, 18 novel 5,6‐dihydrotetrazolo1,5‐cquinazolines were synthesized, their identity, purity, and structure were elucidated by elemental analysis, IR, LC‐MS, 1Н, and 13C NMR spectra. According to the computational estimation, 15 substances were found to be of toxicity Class V, two of Class IV, and only one of Class II. The in vitro serial dilution method of antimicrobial screening against Escherichia coli, Staphylococcus aureus, Klebsiella aerogenes, Pseudomonas aeruginosa, and Candida albicans determined b3, c1, c6, and c10 as the “lead‐compounds” for further modifications to increase the level of activity. Substance b3 demonstrated antibacterial activity that can be related to the calculated high affinity toward all studied proteins: 50S ribosomal protein L19 (PDB ID: 6WQN), sterol 14‐alpha demethylase (PDB ID: 5TZ1), and ras‐related protein Rab‐9A (PDB ID: 1WMS). The structure–activity and structure–target affinity relationships are discussed. The targets for further investigations and the anatomical therapeutic chemical codes of drug similarity are predicted.