Fundamental analytical conditions of the combustion method for the determination of mercury was examined. This method consists of the combustion of the material, collection of mercury as gold amalgam, and regeneration of mercury. In the determination of total mercury in fish tissues, sea and river bottom sediments, it has been clarified that the recovery of added mercury was not quantitative when the material was not pretreatment, but quantitative if treated beforehand with alkali. The method was markedly interfered by various acids such as sulfuric, nitric and hydrochloric acids. Therefore, in the determination of total mercury in fish tissues and bottom sediments, in which acid components are usually contained, the recovery became quantitative by addition of an alkaline solution to the material. Analysis on one material is completed within about 15 minutes, so that this method becomes more effective in the simultaneous treatment of a number of materials.