Abstract: Kier's molecular shape indices(¹K,² K) are calculated for 165 nonionic organic compounds.On the basis of the characteristics of substituents and conjugated matrix,a novel molecular structure parameter-benzene ring factor(G) is defined and calculated for 165 molecules in this paper.A satisfactory relationship between the fish bio-concentration factor(B_CF) of 122 nonionie organic compounds and ¹K,G is expressed as:lgB_CF=-1.433+0.401¹K+1.897G,R=0.955,F=623.47,S=0.454,which could provide estimation and prediction for the B_CF of nonionic organic chemicals.Furthermore,the model is examined to validate overall robustness with Jackknife tests.All these regression results showed that the new parameter G and molecular shape indices have good rationality and efficiency for the fish bio-concentration factor.It is concluded that the ¹K,²K and G will be used widely in quantitative structure-property/activity relationship (QSPR/QSAR) research.