Hemoglobin is the major component of red blood cell and as an allosteric tetrameric protein; it has an important role in carrying oxygen from lunge to different tissues. Hemoglobin was initially thought to reversibly bind only with oxygen, but they were later shown to react with other gasses such as CO and NO and with several organic molecules such as phospholipids and other membrane lipid.Tamoxifen is a non-steroidal anti-estrogen drug that is widely used in the treatment and prevention of breast cancer. It is currently used for the treatment of the both early and advanced ER+ (estrogen receptor positive) breast cancer. Here, interaction between hemoglobin and tamoxifen was investigated at two pH (pH 7.4 and pH 8.4) using fluorescence spectroscopy. Fluorescence measurements were carried out in a Jasco 2500, Hitachi fluorescence spectrophotometer. The excitation wavelength was 280 nm, and the emission spectra were read at 300-600 nm. For describing the fluorescence quenching by tamoxifen using the Stern-Volmer and Scatchard equation. The results of Sten-Volmer and Scatchard plots reveal that KSV and binding constant decreased with increasing pH. The intrinsic Fluorescence of Hb primarily originates from

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