Detailed and systematic studies have been made on the semi-microdiffusion analysis developed by Charley (1945) and by Conway (1943, 1957) for the quantities of carbon dioxide. As a consequence, remarkable improvements have been made on accuracy and precision that have increased the sensibility of the material and simplified the process. The coefficience of variation of the newly improved method is ±0.57% at the 0.8-65.0mg/ml concentration level. In addition, it may be possible to apply techniques of semi-microdiffusion to the problem of fish spoilage.