Acetaldehyde is regulated as a toxic substance in various fields, and the method for monitoring or analysis of acetaldehyde is important. However, handling is difficult because of the high reactivity and low boiling point of acetaldehyde. Therefore, a reference material for high purity acetaldehyde with high accuracy was not available. Although the measuring method of acetaldehyde as a reagent is published in the Japanese Industrial Standard (JIS) where the specification of acetaldehyde purity is more than 80%, the analytical method described in JIS is not enough for an accuracy purity determination method. In this research, the high precision purity determination method for development of a certified reference material (CRM) of acetaldehyde was examined. By controlling the volatility and reactivity of acetaldehyde, we established the purity determination method of acetaldehyde with a relative standard uncertainty of less than 0.3%. Furthermore, this method was applied to develop a high purity acetaldehyde CRM with an expanded uncertainty of 0.005 kg kg(-1) (k = 2).