For the modification of kiln drying schedule, relations between resistance to drying Rd and the moisture content or drying times were found for 4/4, 6/4 and 8/4 green Douglas fir heartwood by the mild drying schedule and the severe drying schedule until the average moisture content was about 10 percent. The results of this study were as follows. 1. Resistance to drying of thicker lumber was higher than that of thinner lumber and resistance to drying of three different thicknesses were negligible between the mild-and the severe drying schedule. The relationships between resistance to drying and two schedules or three thicknesses of lumber were $Rd_1=1.830{ imes}10^5;M^{-2.24}$ for 4/4 lumber by the mild drying schedule, $Rd_2=1.822{ imes}10^5;M^{-2.25}$ for 4/4 lumber by the severe drying schedule, $Rd_3=2.352{ imes}10^5;M^{-2.14}$ for 6/4 lumber by the mild drying schedule, $Rd_4=3.457{ imes}10^5;M^{-2.27}$ for 6/4 lumber by the severe drying schedule, $Rd_5=1.317{ imes}10^6;M^{-2.56}$ for 8/4 lumber by the mild drying schedule, $Rd_6=8.267{ imes}10^5;M^{-2.40}$ for 8/4 lumber by the severe drying schedule. 2. Thinner lumber exhibited lower level of moisture content and shorter drying time required at intersection point between the moisture content and resistance to drying as a function of drying time than those of thicker lumber. Drying time of mild drying was longer than that of severe drying and similar to the level of moisture content at intersection point.