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Nondestructive method of measuring soluble solids content (SSC) of citrus fruits was developed by Fourier transform near infrared (FT-NIR) reflectance and fiber optics. Also, the models describing the relationship between SSC and the NIR spectra of the fruit were developed and evaluated. To develop the models several different NIR reflectance spectra were acquired for each fruit from a commercial supermarket. Different spectra correction algorithms (standard normal variate (SNV), multiplicative signal correction (MSC)) were used in this work. The relationship between laboratory SSC and FT-NIR spectra of citrus fruits were analyzed via principle component regression (PCR) and partial least squares (PLS) regression method using TQ 6.2.1 quantitative software (Thermo Nicolet Co., USA). Models based on the different spectral ranges were compared in this research. The first derivative and second derivative were applied to all measured spectra to reduce the effects of sample size, light scattering, noise of instrument, etc. Different baseline correction methods were applied to improve the spectral data quality. Among them the second derivative method after baseline correction produced best noise removing capability and to obtain optimal calibration models. Total 170 NIR spectra were acquired from 85 citrus fruits and 135 NIR spectra were used to develop the calibration model, the rest spectra were used to validate the model. Developed PLS model, which describes the relationship between SSC and NIR reflectance spectra, could predict SSC of 35 samples with correlation coefficient of 0.872 and SEP of 0.45 Brix.