Measurement of estrogen concentration in bio-samples arevery important for differential diagnosis of various disease orevaluation of health status. However, it is difficult to collectimmediate data of estrogen concentration because they aremeasured by radioimmunoassay or chromatography whichneed time- and cost-consuming sample pre-treatment. Thisstudy was performed for development of new estrogenbiosensor employing taste principles, and for evaluation ofcross reactivity between various steroid hormones. Genesequence of ligand binding domain of α-human estrogenreceptor (amino acid 302-553; hER-LBD) was cloned fromhuman breast cancer cell line. The proteins of hER-LBDwere produced by T7-E.coli expression system, and isolatedby chromatography. hER-LBD were coated on the goldplated quartz crystal (AT-cut 9MHz), and resonance frequencieswere measured by universal frequency counter.Estradiol, progesterone, testosterone, and aldosterone wereused for cross reactivity of the hER-LBD. We also monitoredinfluences of pH change in resonance frequency. The resonancefrequencies of hER-LBD coated quartz crystal weredecreased during increase of estrogen concentration from15 μg/mL to 50 μg/mL. However, similar steroid hormones,progesterone and aldosterone, did not elicit the change inresonance frequency. Testosterone evoke weak change in resonancefrequency. The new estrogen biosensor was moresensitive in pH 7.2 than in pH 7.6. These results suggest thathER-LBD coated quartz crystal biosensor is a probableestrogen biosensor.