4-Quinazolinol was prepared by the reaction of anthranilic acid and formamide. The hydroxy group was converted into the thiol function by treatment with phosphorus(V)sulfide, and the subsequent alkylation of the thiol group was carried out with alkylhalides under the conditions of phase-transfer catalysis. The structure of the substances was confirmed by 1H, 13C NMR, IR, and MS. Most of the synthesized compounds exhibited antimycobacterial activity against the strains of Mycobacterium tuberculosis, Mycobacerium avium, Mycobacterium fortuitum, Mycobacterium kansasii and Mycobacterium intracellulare. 4-(S-Butylthio)quinazoline (3c) was even more active than isoniazide against atypical strains of mycobacteria.