Abstract: The electrotopological state index (Ei),transformed electrotopological state index (EEi) and molecular electronegativity-distance vector (MEDV)  (Mk) were used to describe the molecular structures of 30 substituted phenols and benzoic acids  compounds in this paper,in which EEi= Ei+0.5Qj,Qj = 3x-1.5y,x being the number of -OH,y being the number of -COOH in molecule j.A quantitative linear relationship between biochemical oxygen demand of 30 substituted phenols and benzoic acids compounds and 3-variable model （EE43，E28，M28） was set up using a stepwise linear regression (SLR).The QSBR model is obtained as follows:BOD% = 66.121-3.594EE43+57.028E28-15.049M28,R =0.900.Using leave-one-out (LOO) of Jackknifed method,the model possessed better predictability and robustness.The calculated values were in good agreement with experimental data The equation has shed light on the essencial factors influencing the biodegradability of substituted phenols and benzoic acids compounds.

Key words: electrotopological , state , index;electronegativity-distance vector;biodegradability;biochemical oxygen demand;quantitative structure-property relationship