The interaction of valsartan (VLS), an angiotensin II receptor antagonist, with plasma and bovine serum albumin (BSA) has been investigated at physiological acidity (pH 7.40) by spectroscopic (UV spectrophotometry and fluorescence) techniques. The effect of BSA on UV absorption spectra of valsartan was monitored at three concentration levels of BSA. The binding parameters of VLS-BSA were calculated using non-linear regression analysis of the Scatchard plot. The binding percentages were calculated at different dilution folds of plasma. A strong fluorescence quenching reaction of VLS to BSAwas observed. The binding constants ofVLS with BSA at 288, 298 and 309 K were calculated as 2.624ï´107, 2.431ï´107 and 2.254ï´107 M-1, respectively. The thermodynamic parameters, ïHï° and ïSï° were obtained to be -5.35 ± 0.096 kJ mol-1 and 123.49 ± 0.32 J mol-1 K-1, respectively, indicating the presence of hydrophobic forces between VLS and BSA.