Nitric oxide (NO) is an essential factor in the immune regulation of the host defense mechanisms. In macrophages, NO is produced by inducible nitric oxide synthase (iNOS). Mycobacterium tuberculosis (Mtb) uses different mechanisms for interacting with NO. Some proline-glutamate (pe) and proline-proline-glutamate (ppe) genes of Mtb are known to inhibit NO production. This study aimed to evaluate the expression of pe/ppe genes and to examine iNOS gene expression and NO production in sensitive, rifampin mono-resistant, and multi-drug resistant (MDR) Mtb strains. The expression of pe and ppe genes, including ppe2, pe15, pe5, and pe-pgrs62, was determined by real-time polymerase chain reaction (RT-PCR) assay in 55 clinical isolates and infected THP-1 cell line. Also, the expression of iNOS genes and NO production were evaluated by RT-PCR assay and Griess method, respectively. The significant expression of ppe2, pe15, pe-pgrs62, and pe5 genes (P<0.05 for all) was observed in rifampin mono-resistantand MDR strains, as compared to sensitive strains from clinical isolates and the infected THP-1 cell line. The evaluation of iNOS mRNA showed that the expression of this gene in sensitive strains was significantly higher than MDR strain (P<0.05), while no gene expression was observed in rifampin mono-resistantstrain. Also, NO production in the THP-1 cell line, infected with sensitive strain , increased as compared to MDR strain. Based on the present results, differences in the expression of pe and ppe genes and NO production between resistant and sensitive strains may be helpful in the development of new strategies for controlling resistant tuberculosis.