Abstract: An increase in the bowing rate or slendereness raito of the member resulted in a decrease in the compression strength parallel to grain of the crooked log. The influence coefficient of the bowing rate on the strength between the species was different and showed a curve relation. It may be calculated by a formula of K=98d/(785h+98d)×a, where a is a function of the bowing rate C. The value of a can be confirmed by testing of different species. In this trial, the results are:In the case of C>2.5%, for Eucalyptus exserta a=C(0.61-0.04C), and for Pinus elliottii a=C(0.22+1.42/C). When C<2.5%, for E. exserta a=ln(1.8+1.22C), and for p. elliottii a=ln(2.1+2C)

Key words: Compression strength parallel to grain, Bowing rate, Influence coefficient of bowing rate