Detailed studies have been made on composition and characteristics of clay minerals as well as kaolinization process of feldspar in the Longyan weathe- ring type kaolin deposit of Fujian province by means of X-ray diffraction, infrared absorption spectrometry, analytical electron microscopy, scanning electron microscopy and chemical analysis. The results suggest that the weathering profile of the granite shows distinct vertical zonality and can be divided in downward succession into three zones, i. e.，strongly weathering, weakly weathering and parent rock zones, which make up a typical weathering crust formed by in-situ weathering of the parent rock. The clay minerals in the kaolin deposit are rather simple and consist mainly of kaolin minerals (kaolinite as well as 7A and/or 10A halloysite) and hydromuscovite. Each weathering zone has its own characteristic clay mineral assemblage: the strongly weathering zone and the weakly weathering zone are noted respectively for kaolin mineral-hydromuscovite assemblage and hydromuscovite-kaolin mineral assemblage. The difference in clay mineral composition indicates kaolinization degrees of feldspar at different stages. Studies show that kaolinite in the Longyan kaolin deposit is poorly crystallized and generally assumes irregular flaky form. Book-shaped kaolinite after pseudo- morph of feldspar and large flaky crystals after pseudomorph of mica can also be recognized with grain size generally larger than 2}m. Halloysite is of 7A and/or 10A type and is mostly less than 2μm in granularity;it is characterized by diversity in shape with the tubular form being most common. The apparent unrolling and longitudinal fracturing displayed by many tubules are related to dehydration of halloysite. The conversion of feldspar into kaolin minerals results from the following process: First there is a continuous transformation Series from subspaerical amorphous allophane through spherical or tubular halloysite to hexagonal flaky kaolinite; second，some feldspar is directly altered into kaolin minerals either by solid-state transformation or by crystallization from solutions that have filled etch pits in feldspar. The muscovite-kaolinite transition may take place directly. forming kaolinite after pseudomorph of biotite.