Aim To check the effect of oxidative stress on inductive nitric oxide synthase (iNOS) mRNA expression in macrophages. Methods The effect of tert butyl hydroperoxide (tbOOH) on iNOS mRNA expression in RAW264.7 cells was in vestigated by RT PCR method. Results It showed that, 1.5×10 -4 mol/L tbOOH could induce iNOS mRNA expression in RAW264.7 cells; and the induction could be attenuated by actinomycin D or cycloheximide or acetovanilone added in the medium. Transcription factor NF κB specific inhibitor PTDC could also reduce the induction. Conclusions It indicated that, tbOOH could transcriptionally induce iNOS expression in RAW264.7 cells, de novo protein synthesis and intracellular superoxide (O 2 -·) production might be involved in the process. The activation of NF κB was also one part of the process.