DOM is an essential component in aquatic ecosystems due to its active involvement in element flow and cycling, thus there is a critical need to better understand its biogeochemical behaviors and chemical composition. However, DOM is so structurally and molecularly complex that even the most advanced analytical techniques are often biased towards certain groups of compounds depending on the specific technique or means of extraction. Expanding our tool box, therefore, is often necessary to gain a more comprehensive picture of the DOM. Here I’ll present a novel technique we have been developing recently to analyze DOM, i.e., thermal slicing ramped pyrolysis gas chromatography–mass spectrometry (TSRP-GC/MS). In TSRP-GS/MS, a single sample can be consecutively pyrolzed in multiple thermal slices that are preselected, thus two dimensional information can be obtained, one with GC elution time and the other with thermal slices. In this talk, I will present results from a set of DOM samples from riverine and oceanic environments. The preliminary results show that TSRP-GC/MS has great promise in offering molecular and structural information of DOM in a semi-quantitative way, including the linking between biolability and thermal lability of DOM.