Mollisol samples were incubated indoors with ¹³CO(NH₂)₂ as substrate to investigate transformation of urea-carbon into soil amino sugar and its effect on dynamics of amino sugar pool. Contents of the three types of amino sugars (glucosamine, galactosamine and muramic acid) and their enrichments of ¹³C were measured with gas chromatography/mass spectrometry. On such a basis, specific utilization of urea-carbon by different microbial communities was evaluated. Results show that urea-carbon might be assimilated by soil microorganisms, but was significantly lower in availability than glucose-carbon. A higher amount of ¹³C was found in glucosamine than in muramic acid, suggesting that fungi are more capable of assimilating urea-carbon than bacteria. Application of urea decreased soil organic carbon content to some extent and at the same time significantly lowered the total amino sugar and its relative proportion in soil organic carbon, indicating that in severe shortage of carbon sources, amino sugars would be the priority carbon source to be decomposed to make up the carbon supply. Although muramic acid was very low in concentration, it was highly capable of regulating and balancing carbon budget. Glucosamine was more stable than muramic acid, but decomposition of some of it was found in shortage of other carbon sources. As a whole, the dynamics of amino sugars is closely associated with the availability of soil carbon sources and their coupling effect, thus playing an important role in regulating supply and requirement of carbon and nitrogen in soil.