The high temperature deformation behavior of the activated sintered W powder compacts was investigated. The W compact showed the relative density of 94% with the average W grain size of $23mutextrm{m}$ by activated sintering at $1400^{circ}C$ for 1 hour. Compression tests were carried out in the temperature range of $900-1100^{circ}C$ at the strain rate range of $10^{0}$/sec - $10^{-3}$/sec. True stress-strain curve and microstructure exhibited the grain boundary brittleness which was dependent on the compression test temperature. The activated sintered W compact showed that the maximum stress as well as the strain at the maximum stress was abruptly decreased as the test temperature increase from $900^{circ}C$ to 1000 and $1100^{circ}C$ regardless of the strain rate. The discrepancy of the microstructure in the specimen center was obviously observed with the increase of the test temperature. After compression test at $900^{circ}C$ the W grain was severely deformed normally against the compression axis. However, after compression test at $1000^{circ}C$ and $1100^{circ}C$ the W grain was not deformed, but the microcrack was formed in the W grain boundary. The Ni-rich second phase segregated along the W grain boundary could be partly unstable over $900^{circ}C$ and affect the poor mechanical property of the activated sintered W compact.