Paddy rice field extraction is one of the applications of satellite remote sensing. Full polarimetric synthetic aperture radar is capable of distinguishing between crop types based on the differences in their scattering characteristics. ALOS-2 PALSAR-2 data acquired in early August over a Japanese agricultural area were analyzed to distinguish paddy rice fields from other crops, such as soybean, corn, and vegetables. The scattering characteristics of these crop types were clearly different. The threshold analysis method using polarimetric decomposition parameters examined by a previous study was employed. The results exhibited misclassification of vegetable open culture fields as paddy rice fields. The effect of the variability in the structure of vegetable fields on the scattering mechanism should be considered for improvement of the crop classification method using polarimetric decomposition parameters.