Introduction and objective: The potential risk of application of high dosage of traditional medicinal plants has not been fully understood. Appropriate microbial biosensors have been constructed for monitoring the toxicity of many harmful chemical compounds. The aim of this research was to see how effective are the different concentration of two medicinal plants extracts (Crocus sativus (saffron) and Cannabis sativa) on a bioluminescent marker system indicating their side effects. Materials and methods: The stability and light intensity of Escherichia coli SM10 λpir were previously characterized and confirmed. Several concentrations of saffron and cannabis water extracts were prepared. The light intensity was measured for a mixture of 450μl of aqueous saffron extract and 50μl of biosensor using a luminometer. Results: Results showed gradual decrease on light output in the way that luminescence decreased from 538859 RLU/s for 0.001g/ml aqueous saffron extract to 4830 RLU/s for 0.2g/ml concentration. Although induced increase in bioluminescence was observed for low concentration (0.001 and 0.01 v/v) of cannabis extract 0.25 and 1v/v concentration showed significant decrease in bioluminescent activity. Calculation of % INH of luminescent indicated the correct sensitivity of luminescent biosensor E. coli SM10 S1 to various concentration of saffron and cannabis extracts. Conclusion: The results show the appropriate interaction of constructed biosensor to different concentrations which can be used for further investigation on other ranges of concentrations. Application of luminescent microbial biosensor for investigation of the quality of products such as saffron and cannabis is new.

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