Abstract: This article deals with the diagenesis and micropores of micrites in the Palaeo-zoic and Mesozoic marine carbonate sequences from the middle and lower Yangtze area. The micrites are characterized by simple original composition. fine grain, low porosity and permeability. They are not considered commonly as reservoir rocks. Our preliminary studies show that diagenetic processes such a pressure solution dissolution. penecontemporaneous dolomitization. late dedolomitization. and desilicifiation have contributed to the develop merit of micropores and even visible pores. The micropores formed during sedimentation and diagenesis can be distinguished into primary and secondary types, and the majority of microfissures are caused by dissolution and pressure solution. The anionnt of such pores and fissures increases with increasing intensity of constructive diagenesis. Although their practical significance to the reservoir rocks is not ye clear enough. the well development of the micropores and their connectivity could be considered as an indication for the possibility that these micrites wil1 become reservoir rocks. and hence they deserve further investigation.