Carbonate reservoir of Zhujiang Formation in Pearl River Mouth Basin is rich in oil and gas resources. Previous studies have focused on sedimentary environment and evolution, geological structure, sequence stratigraphy, and so on, with little reference to carbonate diagenesis. We made a detailed study of the petrologic and geochemical characteristics of carbonate rocks in Zhujiang Formation.Methods: Based on detailed petrographic observation, cathodoluminescence (CL) analysis and carbon and oxygen isotopic analysis, we have studied the carbon and oxygen isotopic compositions and diagenesis of carbonate rocks in Lower Miocene Zhujiang Formation, Pearl River Mouth Basin.Results: The results show that: ① δ13C(PDB) values of whole rock carbonate samples of Zhujiang Formation are mainly distributed between -2‰~2‰, consistent with that of benthic foraminifera in the same period, reflecting the same carbon source with Early Miocene seawater. ② Samples abundant equant and blocky calcite cements from Liuhua area are with significant more negative δ13C(PDB) as low as -7.2‰. The δ13C（PDB） and δ18O（PDB） of these samples show good positive correlation (coefficient greater than 0.6), and good correlation also between the δ13C of whole rock and the content of cements, indicating that the negative excursion of carbon isotope is caused by cementation. ③ Diagenetic sequence analysis reveals that equant and blocky calcite cements are precipitated in middle—deep environments. The average δ13C（PDB） and δ18O（PDB） of 5 blocky calcite cements are -13‰ and -8‰, respectively, which confirm that the cements formed during burial condition result in the lower carbon isotope value, and the carbon source is possibly originated from organic acids.Conclusions: Organic acids sourced from burial diagenesis effect mainly contribute to the significant more negative δ13C and δ18O of Zhujiang carbonates in Liuhua area, providing some new information for understanding the relations between carbonate diagenesis and reservoir development and evolution.