Elemental analyzer - isotope ratio mass spectrometry (EA-IRMS) is the most popular method for the measurement of sulfur isotopes in various samples including sulfide, sulfate and organosulfur compounds. The precision of ~±0.3‰ (1σ) can be achieved for samples with ~100 μg S. However, for samples with low sulfur content, or organic matter in particular (e.g., animal bone collagen), the precise and accurate sulfur isotope analysis remains challenging, with typical δ34S precision ranging from ±0.3‰ to ±1‰. In this study, we applied an improved EA-IRMS with a custom-built cryofocus device for the analysis of sulfur isotopes in organic matter. After sample combustion, all the product gases were transferred into a cold trap by a fast helium flow (100 mL/min). SO2 was then separated from other gases through a packed gas chromatographic (GC) column at lower flow rate (10 mL/min). The sample size of this method is ~300 nmol S, which is only 1/10 of that required by the conventional method. Lowered sample size allows fully oxygen isotope homogenization of sample SO2 with oxygen buffers during combustion. With this method, the δ34S precision from the measurement of organosulfur standards was better than ±0.3‰.