The molecular volumes of dioxins,organic phosphorous compounds and n-alkanols were computed at the B3LYP/6-311G** level,and were then correlated with their toxicity.It was surprisingly found that there exists the so-called“critical volume of toxicity”(CVT)in each series of compound of the present study,i.e.the toxicity increases with increase of the molecular volume when less than CVT,while decreasing with increase of the molecular volume when lar-ger than CVT.The CVT for the three series of compounds is quite similar,ranging 0.309—0.320nm3.It was proposed that the ordinary linear solvation energy relationship (LSER) should be modified with respect to the new findings,and ac-cordingly the anaesthetic potency of partial fluorinated n-alkanols was predicted. The molecular volumes of dioxins, organic phosphorous compounds and n-alkanols were computed at the B3LYP / 6-311G ** level, and were then correlated with their toxicity. It was surprisingly found that there exists so so-called “critical volume of toxicity ”(CVT) in each series of compound of the present study, iethe toxicity increases with increase of the molecular volume when less than CVT, while decreasing with increase of the molecular volume when lar-ger than CVT. CVT for the three series Of was similar that ranging from 0.309-0.320 nm 3.It was proposed that the ordinary linear solvation energy relationship (LSER) should be modified with respect to the new findings, and ac-cordingly the anaesthetic potency of partial fluorinated n-alkanols was predicted .