We have already measured ground clutter using an X-band and L-band radars. Here, ground clutter was first measured using a millimeter wave radar with the frequency of 34.86 GHz, which is located on the campus of the University of Electro-Communications. The pulsewidth of the radar was 30 ns. Thus the spatial resolution was as small as 4.5 m. We have found that the clutter amplitude distribution obeys a Weibull distribution with shape parameter of c0.497 to 0.675 at depression angles of 0.8 to 1.9 deg., when reflectors are ordinary terrain and such structures as landing strips at airport and buildings. To improve target detectability in such Weibull-distributed ground clutter, Weibull constant false alarm rate (CFAR) system will be required.