Monitoring variation in the crustal strain in space and time is a key to understand the physical process in the crust and to forecast the crustal activity. A dense array of continuous GPS tracking network provides us with one of the ideal tools for monitoring crustal strain. In Japan, the Geographical Survey Institute (GSI) started to establish a dense GPS array in the Kanto-Tokai region in 1992 and has further expanded it to cover the entire nation. The GSI has been operating 610 sites, for continuous monitoring of the daily site coordinates since April, 1996. The number of sites went up to about 1000 by 1997. The average site interval is about 20 km (eg, Miyazaki et al., 1997). The array is now considered as one of the most dense and fundamental infrastructures for monitoring crustal activity in the Japanese Islands. Miyazaki et al.(1998) estimated the displacement field of the Japanese Islands relative to the stable interior of the Eurasian plate by analysing the data from this network. The results indicated a prominent westward motion of the northeastern part of Japan and a northwestward movement of the southwestern part of Japan. This clearly due to the effects of the subducting oceanic plates under the Japanese Islands. In the present study, we try to delineate the crustal elastic and inelastic strains of the Japanese Islands, using two years data from the above GPS array (Fig. 1). One problem in providing the strain field using geodetic data is due to the assumption that the Japanese Islands deform elastically in time and our inability to detect the inelastic properties of the crust that may be relevant to earthquake prediction. However, evidence from geology and geomorphology suggests that the crustal deformation is not purely elastic, especially for long time intervals. Thus estimation of the inelastic properties of the crust is important to collaborate the deformation with geomorphology. Moreover, the