Thepotassium dihydrogenphospiate (KDP) intercalated kaolinite (K-KDP) was prepared by a three-step reaction. Firstly, polar dimethyl sulphoxide (DMSO) was introduced into the layers of kaolinite by ultrasonic method and the product K-DMSO was obtained as precursor; secondly DMSO was replaced by potassium acetate (KAc) and the product K-KAc was gotten as intermediate; finally KAc was replaced by KDP. The intercalation ratio of the final product K-KDP reached 81.3%. The structure of products at differentreaction process was characterized by Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM) in detail. FTIR results showed the existence of P==O in the final product but moved from 1300 to 1201 cm(-1). XRD results documented that the interlayer spacing of kaolinite was enlarged during the whole intercalation reaction. SEM indicated that the agglomeration of kaolinite was destroyed and the particle size distribution became more uniform.