Research on trace elements has been paid attention recently. In order to determine concentrations of various kinds of trace elements in biological materials, atomic absorption spectrophotometer is widely used. This instrument allows single element analysis at ppb levels. Microwave induced plasma-mass spectrophotometer (MIP-MS) or inductively coupled plasma-mass spectrophotometer (ICP-MS) permits multielement analysis at sub-ppb or ppt levels. These analytical instruments accept liquid samples only. Biological materials such as organs, tissue and blood must be digested in prior to apply into the instrument. Digesting methods, simplified wet ashing and microwave ashing are introduced.