Abstract: The time and quantity of N fertilization is considered as a key technique for high yield and quality in crop production. Based on the rice field experiment with different N rates, the mid-IR transmittance spectra of the dried and ground leaf samples were determined by Fourier transform infrared (FTIR) spectroscopy, and then the estimation model for leaf nitrogen content was built with the obtained mid-IR transmittance spectra and synergy interval partial least square algorithm (siPLS). The optimal siPLS model was obtained with 100 intervals and 9 PLS components. The best combinations of spectral regions selected were 1350.89–1586.57, 1587.53–1822.40 and 3709.41–3943.72 cm-1. The value of RMSECV (root mean square error of cross-validation) is 0.1538, and correlation coefficient (r) was 0.9393 in calibration set, and the RMSEP (root mean square error of prediction) was 0.1933 and correlation coefficient (r) was 0.6649 for test data set. Furthermore, compared with spectral indices NFS and NFSA, this model was more reliable and representative. It was suggested that FTIR spectroscopy may be considered as a diagnosis technology for leaf nitrogen content in rice.