For pollution control of the ocean and in the research of the ocean environment, the measurement of total organic carbon (TOC) is regarded as an important index of organic contaminants contained in seawater. At the same time, the measurement of total nitrogen (TN), which is known to cause eutrophication, is also attracting attention for environmental pollution control and in ecological research. Seawater has an NaCl content of approx. 3.5 %. Shimadzu's TOC-L combustion method total organic carbon analyzer allows accurate measurements of TOC directly from samples containing a high concentration of inorganic salts without any pretreatment such as dilution. In addition, by installing the TNM-L total nitrogen unit, TN measurement is also enabled. This makes possible simultaneous measurements of TOC and TN. This article introduces an example of simultaneous TOC/TN measurements of seawater, using Shimadzu TOC-LCPH combustion method total organic carbon analyzer and TNM-L total nitrogen unit.