The major parameters affecting the accurate and precise determination of lead isotopic ratios by multiple collectors inductively coupled plasma mass spectrometry(MC-ICP MS) were investigated.In the optimized conditions,the relative standard deviations(RSDs) of lead isotopic ratios for NIST SRM 981 standard solution by thirty repeated determinations in 10 h at lead concentration of 4 ng/mL were about 0.005% for 208Pb/206Pb,0.004% for 207Pb/206Pb and 0.054% for 206Pb/204Pb,respectively.Long term stability was tested and the standard deviations(2SD) of 208Pb/206Pb,207Pb/206Pb and 206Pb/204Pb were 0.000 06,0.000 05 and 0.006 7,respectively.A method of NEPTUNE MC-ICP MS for the analysis of stable lead isotopic ratios in trace lead marine carbonates was developed.Hainan corals(Porites lutea) and giant clams(Tridacna gigas) were analysed,the procedural blank of 8-10 pg and the errors of repeated samples better than 0.1% were obtained.After eluted with 0.50 mol/L HNO3,208Pb/206Pb and 207Pb/206Pb in Hainan corals were determined to be 2.086 2 ± 0.001 5 and 0.849 90 ± 0.001 47(n=16),respectively,and 208Pb/206Pb and 207Pb/206Pb in Hainan giant clams were 2.116 9 ± 0.004 2 and 0.864 81 ± 0.001 62(n=9),respectively.The 204Pb ratios of marine carbonates in South China Sea were also reported.The results showed that the lead isotopic ratios of marine carbonates in South China Sea were related to Chinese aerosols,atmospheric deposits of Pearl River Delta,loess,basalts from the South China Sea,etc.The method could be applied in the determination of lead isotopic ratios in marine carbonates that have low lead concentration but complicated matrix with high calcium concentration.