Fourier transform infrared spectroscopy(FTIR)technique was applied in the early detection of corynespora spot on cucumber leaves while the symptom had not appeared. The cucumber leaves were inoculated with Corynespora cassiicola. By observing the changes in the FTIR spectra of infected cucumber leaves at various times of post-infection, three sensitive bands, 1 735, 1 545 and 1 240 cm-1 were selected for the identification of cucumber corynespora leaf spot. According to the peak areas at these sensitive bands, cucumber leaf samples infected with C. cassiicola and control uninfected leaf samples could be classified correctly. Results clearly demonstrated that the FTIR technology is an available one for the early detection of corynespora spot on cucumber leaves while the symptom has not appeared and it provides a new method for the early detection of corynespora spot.