This paper describes outlines and first results of measurements and analysis of residential PV systems in the Japanese monitoring program commissioned to JET and AIST by NEDO (New Energy and Industrial Technology Development Organization) started in FY2001. The objective of this research is to collect actual operational data of various residential PV systems installed in Japan and to conduct the analysis and the evaluation necessary to develop the "total support technology for PV systems". In addition to the existing 100 monitoring systems, some more monitoring systems are going to be installed by FY2003, in which new measurement items such as inverter output voltage and separate information of multiple -plane arrays are added to evaluate the restricted inverter output and multiple-plane array systems.