We examined relationship between forest parameters and /spl sigma//sup 0/ derived by airborne multi-polarization SAR (PiSAR). PiSAR observations and field measurements were simultaneously performed on November 2002 and August 2003. One data set was taken from stands with pure pine (Picea glehnii Masters) forest. More than 70% of the trees in biomass are Picea glehnii Masters in the data set with same stand age. The other data set was taken from the stands where mixture of species is proceeding in some degree. The former data set shows more tight correlations compared to the other and correlation coefficient reaches 0.98. We conclude that (1) the mixture of the species and stand age are two of the major reasons of data scattering between forest parameters and /spl sigma//sup 0/, and (2) the above ground biomass saturation level is about /spl sim/150 tons/ha for L-band /spl sigma//sub HH//sup 0/ and /spl sigma//sub HV//sup 0/ and /spl sim/70 tons/ha for /spl sigma//sub VV//sup 0/ in this akaezomatsu site, using a biomass expansion factor of 1.36 to convert from the trunk biomass to the above-ground biomass.