Huge amount of ash is generated from industrial wastes. In order to recycle this, the production of glass powder from ash is very useful because the use of glass powder as filler for concrete improves its properties. The purpose of this study is to clarify the formation mechanism of glass powder from powder ash and to obtain an optimum condition for its production. In this study, three kinds of ashes (sewage sludge ash, paper sludge ash, and coal ash) were used for the production of glass powder. Glass fraction and the ratio of spherical particles for the glass powder were measured. The crystalline phases in the glass powder was identified, and melting behavior of the ashes was investigated. It was found that melting process is very important to produce spherical glass powder and that the basicity defined as the ratio CaO/SiO2 is a good measure to control the composition of the ashes for the glass powder production.