Bending tests were performed on full scale structural lumber sawed frm sugi(Cryptomeria japonica D.Don.) logs grown in Oita orefecture, and the relationship between the wood's strength performance and material factors, as well as the variation of Young's modulus in the wood in its transformation from log to lumber were examined. The ersults are summarized as follows. (1)The mean value of MOE (A) (modulus of elasticity corrected by the standard testing condition) and MOR(A) (modulus of repture correcetd by the standard testing condition) of the sugi square-cut lumber were 7.86kN/mm2 and 40.3N/mm2, respectively. On the ither hand the mean value of MOE(A) and MOE(A) of the sugi rectangular-cut lumber were 8.12kN/m2 and 47.7N/mm2, respectively. The MOE(A) values in both sugi lumber were above the value of standard strength of non graded lumber of established by the Ministry of Construction notice. (2)In the relationship between material factors and strength performance,MOE(A) showed the highest correlation to MOE(A). It was proven that in full-scale boxed heart square-cut structural lumber of sugi the effect of the knots on the strength was small. (3)The dynamic modulus of elasticity decreased in the transition from log to gren lumber. It is considered that sawing pattern and the ratio of juvenile wood in the lumber are involved in the reduction of this value. (4)The machine stress grading of the JAS (Japanese Agricultural Standard) using modulus of elasticity approximately corresponded with the value established by the Ministry of Construction notice. This sugegsts that lumber grown in Oita prefecture classfied according to the grading scale of the JAS can be utilized in terms of its strength preformance.