Abstract: Middle Cambrian oolitic carbonate rocks were deposited in small shoals of the ramp in a central ancient upwelling area in the Ordos Basin. The oolitic carbonate rocks mainly consist of calcites and dolomites. The δ¹⁸O and δ¹³C values range from -11.3‰ to -4.9‰ and from -1.7‰ to 0.3‰, averaging -6.5‰ and -0.8‰ V-PDB, respectively. Since they were deposited in oolitic shoals under meteoric leaching and experienced deep burial diagenesis, the δ¹⁸O values of the oolitic carbonate rocks are obviously low. During diagenesis, the influence of organic materials was slight, leading to normal δ¹³C values for the oolitic carbonate rocks. The δ¹⁸O values of dolomites are higher than those of limestones. The results of analyses by laser-microsampling indicate that the δ¹⁸O and δ¹³C values of ooids are lower than those of the cements because the ooids formed in turbulent environments, and were leached by meteoric water after their formation. The cements precipitated in pore water with marine characteristics and high salinity, and were slightly influenced by meteoric water after their formation. The oolotic carbonate rocks are characterized with low Na and Sr, very high Fe, and medium Mn contents because of deep burial diagenesis. Most dolomites with low order degrees and high MgCO₃ contents generally formed through replacement in brine during the burial stage. Deep burial diagenesis and good development of cements resulted in the development of extremely low porosity in the oolitic carbonate rocks.