Several techniques were used to identify and classify plants. Mid-infrared spectroscopy combined with appropriate software was used in an attempt to differentiate different subgenus from Rhododendron. Fourier transform infrared (FTIR) spectroscopy was used for obtaining vibrational spectra of 46 petals from Rhododendron. Very minor differences were observed in the FTIR spectra among four subgenuses. For the purpose of rapid differentiation, libraries of spectra were created using samples from each subgenus variety. Spectra of unknown samples were recorded and compared with those of the libraries and the rate of affinity (the match value) was measured automatically using the appropriate software (OMNIC). The results showed that petal samples from different subgenus varieties can be differentiated from each other. The study demonstrates that combining FTIR spectroscopy with appropriate analysis method can classify Rhododendron plants at subgenus level. It offers a potential method for the taxonomic research on plants system.