Two pairs of primers were designed. Nine isolates of isoniazid-sensitive and 11 isolates of isoniazid-resistant M. tuberculosis were analyzed by polymerase chain reaction amplification of 396 bp sequence of katG gene. With the use of single-strand conformation polymorphism analysis and DNA sequencing, 8 isolates in 396 bp products and 5 isolates in 216 bp products of the 11 isolates showed point mutations and no deletion or insertion was detected. Thus, in China, point mutations in katG gene can mainly account for inactivation of catalase-peroxidase, leading to isoniazid resistance. The results provide laboratory evidence for detecting the isoniazid resistance in M. tuberculosis and also explore its molecular mechanism.