The aim of this study was to use DNA sequencing analysis to analyze the mutations in the most commonly targeted genes (katG, inhA, rpoB, rpsL) in isoniazid (INH)-, rifampin (RIF)- and streptomycin (SM)-resistant Mycobacterium tuberculosis strains obtained from subjects in Düzce, Turkey. Four isolates were found to be INH-resistant, 3 were RIF- resistant and 5 were SM-resistant, out of a total of 52 M. tuberculosis strains. In 3 of the 4 INH-resistant strains, a mutation in the katG gene in codon 315 appeared as AGC → ACC (Ser → Thr), and the other INH-resistant strain showed a mutation in the katG gene in codon 314 as ACC → CCC (Thr → Pro). There were no mutations in the inhA gene in INH-resistant isolates. Two of the 3 RIF-resistant strains were found to have mutations in the rpoB gene in codon 516 appearing as GAC → GTC (Asp → Val), and the other RIF-resistant strain has a mutation in the rpoB gene in codon 531 as TCG → TTG (Ser → Leu). These 3 RIF-resistant strains are also INH-resistant. All 5 SM-resistant strains have mutations in the rpsL gene in codon 43 appearing as AAG → AGG (Lys → Arg). Thus, we found common gene mutations that bring about the resistance of M. tuberculosis to antituberculosis drugs in all of our isolates from Düzce. To the best of our knowledge, the ACC → CCC (Thr → Pro) mutation in the katG gene in codon 314 has not been previously defined.