The interaction between progesterone and human serum albumin has been investigated. This interaction was studied by UV-absorption and fluorescence spectroscopy. From spectral analysis progesterone showed a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constant (K) is estimated 6.56×102 M-1 at 293 K. FT-IR spectroscopy with Fourier self-deconvolution technique was used to determine HSA secondary structure and progesterone binding mechanisms. The observed spectral changes indicate the formation of H-bonding between progesterone and HSA molecules which can be related to the intensity decrease in the absorption band of α-helix relative to that of β-sheets