Several factors sensitive to sediment COD are experimentally investigated, concerning with the pre-treatment of sediment, and with the heat processing of the chemical analysis. The pre-treatment of the sediment is carried out with connection to the water content and the exposure time with the atmosphere. The heat processing of the analysis is investigated with respect to the oxydation property of the sediment and the heating period. As the results of the investigation, the following items are clarified; i) the conventional heating period, 15 minutes, is not enough to obtain a reasonable value of sediment COD, and should be extende to 30 minutes, ii) the cooling period after the hearing would be senstive to the COD value, iii) water content of the sediment should be adjusted by the consideration of the dry weitht and the plasticity, iv) the dehydration of the sediment is recommendable to use the sentrifugal separator from the viewpoint of the protection against atmospheric oxydation, and v) the linear regression of the dry weight of the sediment to the titration mass of Sodium thiosulfate (Na2S2O3) can conveniently modify the measured value and determine the stable value of COD.