This paper presents an improved Schiffman phase shifter with low insertion loss for millimeter-wave applications. Schiffman phase shifter has the advantages of simple structure, clear design idea and excellent phase-shifting characteristics, which is widely used in various microwave systems. However, with increasement of frequency, the energy loss of the coupled-line section on microstrip structure cannot be ignored. Our preliminary research indicates that the insertion loss of the microstrip circuits with coupled structures can be highly reduced by overlaying the artificial magnetic conductor (AMC). To verify the design concept, two kinds of Schiffman phase shifters, namely, traditional Schiffman phase shifter and improved Schiffman phase shifter are designed and implemented at 15 GHz. Measured results show insertion loss can be reduced by 60%.