This paper studied the mineralogical characteristics of kaolin from Longyan by means of chemical analysis, mineral examination, SEM, XRD, IR and DTA-TG. It is shown that the content of Al2O3 and SiO2 is very close to the theoretical value, with tiny content of Fe and Ti. The content of K2O is higher because of residual mica. The results also show that Longyan kaolin is made up of kaolinite with minor mica and a very small amount of quartz, and its natural whiteness varies from 83% to 92%. The SEM photographs of Longyan kaolin show clear layer structure 0.1～5 μm in size, and a small amount of rod-shaped kaolinite. The laser particle size analyzer measurement results of Longyan kaolinite shows that 83.2% particles are between 1.00 and 5.00 μm in size, with an average of 3.16 μm. The main bands of XRD pattern of Longyan kaolinite are 1.004 nm， 0.722 nm，0.447 nm，0.359 nm，0.335 nm，0.257 nm，0.250 nm and 0.235 nm. A comparison with the standard spectrum shows that kaolin is the main mineral component of Longyan kaolin. The 1.004 nm band is attributed to halloysite or mica. Combined with SEM results, these data indicate that Longyan kaolinite contains small amounts of halloysite, and the 0.335 nm band is attributed to quartz. Its lower crystallinity index (HI=0.42) suggests that Longyan kaolinite is a relatively disordered kaolinite. FT-IR spectra imply that the functional groups of kaolinite layer structure remain perfect, but the intensity of 3695.39 cm-1 band (inner surface hydroxyl stretching vibration) is 1.10 times that of 3620.26 cm-1 band (inner hydroxyl stretching vibration), which indicates that the crystallinity of Longyan kaolinite is relatively low. TG results show that the weighloss at 100～800℃ is 11.33%, almost equal to the theoretical water content (10.8%). This also proves that the content of impurities of Longyan kaolinite is tiny. In the present experiments, the Kln-KAc intercalates were investigated to study the relationship between the microstructure and the intercalation. XRD data show that potassium acetate could directly insert between the inner layers of kaolinite. As a result, the c-axis spacing (d001) of Kln-KAc intercalation composite increased from 0.7223 nm to 1.3929 nm of kaolinite, and the intercalation rate could reach over 90%. There were four new bands, 1605.22 cm-1, 1566.33 cm-1, 1416.57 cm-1 and 1344.99 cm-1, on the FT-IR spectrum of Kln-KAc, which indicated that potassium acetate inserted the inner layers of kaolinite. IR analysis showed that the band of inner surface hydroxyl and inner hydroxyl stretching vibration became greatly weaker, and moved towards low wavelength. Synchronously, the appearance of the band at 3604.68 cm-1 was corresponding to the hydrogen bond formed between acetate ions and the inner surface hydroxyl of kaolinite. DTA curves of Kln-KAc indicate the endothermic peak was at 562.05℃, which was attributed to the fact that dehydroxylation became obviously weaker. These data indicated that the microstructure of hydroxyl was destroyed to a certain extent because of the insert of acetate ions. These results indicate that acetate ions insert between the inner layers of kaolinite under the participation of water, and different intensities and types of hydrogen bonds exist between acetate ions and the inner surface hydroxyl of kaolinite.