Organic matter and organic acid are rich in kaolinite rocks in coal measures. Terrestrial plant debris, amorphous organic matter, fulvic acid (FA) in the soft kaolin clay associated with weathered coals and ultramicro-organisms and their burrows are identified in kaolinite rocks in Late-Palaeozoic coal measures of North China. Modeling experiment by using organic acid reacted with aluminosilicate minerals shows that fulvic acid has a great ability to dissolve the aluminosilicate minerals and to accelerate the transformation and crystallization of kaolinite. The author suggests that organic matter and organic acid play an important role in the formation of kaolinite rocks in coal measures. Organic matter and organic acid are rich in kaolinite rocks in coal measures. Terrestrial plant debris, amorphous organic matter, fulvic acid (FA) in the soft kaolin clay associated with weathered coals and ultramicro-organisms and their burrows are identified in kaolinite rocks in Late -Palaeozoic coal measures of North China. Modeling experiment by using organic acid reacted with aluminosilicate minerals shows that fulvic acid has a great ability to dissolve the aluminosilicate minerals and to accelerate the transformation and crystallization of kaolinite. The author suggests that organic matter and organic acid play an important role in the formation of kaolinite rocks in coal measures.