Near-infrared differential absorbance spectra from pure water have been measured for phosphate buffer solutions (pH = 7.4) of human serum albumin (HSA) in the wavelength range of 750-2500nm. The peaks that follow HSA concentration can be observed in near-infrared differential absorbance spectra; in the 1650-1750nm and 2150-2350nm region. The near-infrared spectra in the 750-1350nm, 1550-1850nm and 2052-2500nm regions of the solutions have been subjected to partial least squares (PLS) regression analysis to make calibration models predicting the concentrations of the HSA. The calibration in the concentration range of 0-5g/dl has yielded a correlation coefficient of 0.999 and a standard error of prediction of 0.0283g/dl with latent variable of seven. This result suggests that the near-infrared differential spectra of HSA from pure water reference and its calibration model constructed by using PLS regression can pick up effectively the information about albumin contained in phosphate buffer solutions. This result can be a base of reagentless measurement of HSA in human serum and in vivo HSA measurement.