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Introduction: Ciprofloxacin is a broad-spectrum antibiotic and a member of fluoroquinolones. Its main target in Escheichia coli is DNA gyrase. Ciprofloxacin induces the SOS response via RecA. The presence of RecF protein is essential for RecA activity. The recF is increased in the logarithmic phase by its operon promoter and the stagnation phase by its specific promoter. The activity of the specific promoter is dependent on rpoS. This study aimed to evaluate the expression of rpoS in a ciprofloxacin-resistant mutant. Materials and methods: To evaluate the expression of rpoS, cellular RNAs in the early and middle logarithmic phases of growth were extracted. Then, after synthetizing cDNA, the relative gene expression in the wild type and mutant strains was measured by real-time PCR. Results: Results showed that the extracted RNAs were free of contamination and have a suitable quality for the production of cDNA. Moreover, the expression of rpoS in the early and middle logarithmic phases after ciprofloxacin treatment in the high ciprofloxacin resistant mutant was approximately similar to the wild type strain. Discussion and conclusion: In conclusion, it seems that the increased expression of recF was related to the operon promoter, and treatment with ciprofloxacin did not cause the stationary phase-like conditions. [ABSTRACT FROM AUTHOR]