Objective: HSA is the highly water-soluble plasma protein, which is the smallest and most abundant plasma protein in the human body. Oxazepam (O) and Flurazepam (F) include the most frequently prescribed sedative-hypnotic agents. (F) and (O) bind to human serum proteins more than 95%. Investigations show that HSA has an important role as a carrier for diazepins. The interaction of drugs with HSA, which may have important pharmacokinetics implications, has been extensively studied by several workers. Materials and Methods: The binding of two diazepins [Oxazepam (O) and Flurazepam (F)] to HSA was investigated by means of spectrophotometry. The binding isotherms for interaction of (F) and (O) with HSA at 25 °C shows the variation of ν, the average of bound (O) and (F) per HSA molecule, versus log [D]. The corresponding Scatchard plots for these isotherms were driven. They coincide with usual shapes of Scatchard plots and can represent the existence of one binded set. The binding parameters, binding constant and binding capacity of these medicines were obtained from Hill equation. Results: The binding constants of Flurazepam (F) and Oxazepam (O) were determined 0.6 ± 0.1( x105) and 1.4 ± 0.3 (x105) respectively. The binding capacity of (F) and (O) were computed 1 ± 0.1 and 1.3 ± 0.1, and the Hill constant (nH) was obtained 4.076 and 2.44 respectively. The results of this study show, spectrophotometry can be a simple and fast technique to determine the binding constant for some ligands. Conclusion: These values show the binding affinity of (O) is more than (F), on the other hand, the cooperativity of (F); is higher than (O). With regards to the amount of K, binding affinity of (O) to HSA is more than (F). These results can be justified by the amounts of partition coefficient of (O) and (F).

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