This research evaluated the potential of a Fourier transform near−infrared (FT−NIR) spectrometer with a reflectance fiber optic probe for determination of total soluble solids (TSS) content and available acid (VA) in intact peaches. It also investigated the relative performance of the calibration models with different data preprocessing methods (original, first derivative, and second derivative). Reflectance spectra were collected from two opposite sides of individual peaches, followed by standard destructive methods for analyzing TSS and VA of peaches. Calibration models were developed with the use of a partial least squares (PLS) technique. The best calibration model for TSS gave good predictions of TSS, with a coefficient of determination (r2) of 0.916 and a standard error of prediction (SEP) of 0.534. The best calibration model for VA prediction yielded (r2)=0.904 and SEP=0.129. Thus, FT−NIR reflectance can be used to predict the TSS and VA of intact peaches. Based on the results, it was concluded that FT−NIR spectrometry could be an easy to facilitate, reliable, accurate, and fast method for non−invasive measurement of peach TSS and VA.