To understand the mutations of pncA gene in M. tuberculosis isolates, and to evaluate their clinical value.Analyzing the pncA genes in 74 M. tuberculosis clinical isolates with PCR-SSCP and PCR-AS. M. tuberculosis strain H37Rv was used as control.32 drug-sensitive isolates all displayed normal pncA SSCP profile. Of 20 non-pyrazinamide-resistant isolates, 4 had abnormal pncA SSCP profile, in which 2 isolates were sequenced, one was TTC-->TTA mutation at codon 58, another was TGG-->CGG mutation at codon 68. Of 22 pyrazinamide-resistant isolates, 10 displayed abnormal pncA SSCP profile, in which 2 isolates sequenced had TTC-->TTA mutation at codon 58.The mutation of pncA gene is a pyrazinamide-resistant molecular mechanism in M. tuberculosis. Detecting the mutations of pncA genes might diagnose pyrazinamide resistance rapidly in some M. tuberculosis isolates.