Drying of soil specimens in microwave ovens can permit rapid determination of moisture content; such determination is very important in field quality control of earthwork construction. A laboratory study was performed to investigate differences between soil moisture contents based on microwave oven drying and moisture contents developed from conventional drying procedures. For nine materials ranging from dense graded aggregate to highly plastic clays, differences between moisture contents obtained by the two methods were very small, in many cases not exceeding the variability between values obtained from multiple specimens of the same soil mix dried in a conventional oven.