Properties of organic matter existing in deposited sediments in littoral regions are identified based on the ignition behavior of the sediments. In addition, oxidation-reduction (redox) conditions of the sediments were evaluated based on the redox potential (ORP) and the oxygen reduction capacity (ORC). It was found that the proportions of unstable and humic organic matter could be identified based on the ignition behavior by excluding the clay-structural water content in the sediments. Moreover, a strong correlation between ORC and organic matter state was confirmed. The sediment that contained a high ratio of unstable organic matter to total organic matter made larger reductions in the dissolved oxygen concentration. Furthermore, it was possible to determine the amount of reduced substances based on ORC.