Microbial degradation of dissolved organic nitrogen (DON) from advective transport is one of the major nitrogen sources that support the export production in the subtropical gyres. The limited knowledge about the sources and liability of DON hinders our understanding of this important process. In the summer of 2022, on-deck degradation experiment of labial DON derived from diatom incubation was carried out in the north Pacific Subtropical gyre (NPSG). The microbial degradation of dissolved organic carbon (DOC) and DON was monitored in different treatments with the influence of bacteria, viruses, and protozoa. Samples for the nitrogen concentration and stable isotope that release during the degradation were collected for the study of degradation dynamics and impacts. Our results show that DOC was significantly degraded (40%) within five days, and the concentration of ammonium increased by 35% in the same treatment. There is no significant difference in DOC degradation between the treatments with and without viruses. Related chemical and biological parameters would be measured in the future. Our current result shows that the microbial degradation of DON would provide nitrogen source for the producers. And it would be very interesting to learn more about the contribution of nitrogen including the stable isotope signature of this process, as well as its controlling mechanisms.