Dissolved organic matter (DOM) represents a significant source of nutrients that supports the microbial-basedfood web in seagrass ecosystems. However, there is little information on how the various fractions of DOM fromseagrass leaves contributed to the coastal biogeochemical cycles. To address this gap, we carried out a 30-daylaboratory chamber experiment on tropical seagrasses Thalassia hemprichii and Enhalus acoroides. After 30 daysof incubation, on average 22％ carbon (C), 70％ nitrogen (N) and 38％ phosphorus (P) of these two species ofseagrass leaf litter was released. The average leached dissolved organic carbon (DOC), dissolved organic nitrogen(DON) and dissolved organic phosphorus (DOP) of these two species of seagrass leaf litter accounted for 55％, 95％and 65％ of the total C, N and P lost, respectively. In the absence of microbes, about 75％ of the total amount ofDOC, monosaccharides (MCHO), DON and DOP were quickly released via leaching from both seagrass species inthe first 9 days. Subsequently, little DOM was released during the remainder of the experiment. The leaching ratesof DOC, DON and DOP were approximately 110, 40 and 0.70 μmol/(g·d). Leaching rates of DOM were attributedto the nonstructural carbohydrates and other labile organic matter within the seagrass leaf. Thalassia hemprichiileached more DOC, DOP and MCHO than E. acoroides. In contrast, E. acoroides leached higher concentrations ofDON than T. hemprichii, with the overall leachate also having a higher DON: DOP ratio. These results indicatethat there is an overall higher amount of DOM leachate from T. hemprichii than that of E. acoroides that isavailable to the seagrass ecosystem. According to the logarithmic model for DOM release and the in situ leaf litterproduction (the Xincun Bay, South China Sea), the seagrass leaf litter of these two seagrass species could releaseapproximately 4×103 mol/d DOC, 1.4×103 mol/d DON and 25 mol/d DOP into the seawater. In addition toproviding readily available nutrients for the microbial food web, the remaining particulate organic matter (POM)from the litter would also enter microbial remineralization processes. What is not remineralized from either DOMor POM fractions has potential to contribute to the permanent carbon stocks.