Quantitative structure-activity relationships (QSARs) for the toxicity of substituted phenols, anilines and nitrobenzenes to algae (Scenedesmus obliquus) have been studied. Chemicals were divided into polar narcotics and electrophiles based on structure criteria according to the toxicity mechanisms of action. A good relationship between the toxicity and octanol/water partition coefficient (logP) was observed for the polar narcotic compounds. The results confirmed that hydrophobicity is the determining physicochemical parameter in modelling narcotics. However, no statistically significant mono-parametric QSAR models could be made from descriptors calculated in this study for all the compounds. In order to investigate the mechanisms of toxic action and develop QSAR models for all compounds, Abraham solvation descriptors were calculated from the program of Pharma-Algorithms. Stepwise regression produced a three-parameter QSAR model (polarizability/dipolarity, hydrogen-bond basicity and molecular volume) with a good statistical fit for all the compounds studied, which had square of the correlation coefficient R2=0.83. We have also developed an interpretable QSAR model by using parameter of logP, which represents the bio-uptake process, and polarizability/dipolarity (S), which represents the interaction of chemicals with the acceptor micromolecules (target receptor) at the active site. No hydrogen-bond interaction was observed between the chemicals and receptor micromolecules. Quantitative structure-activity relationships (QSARs) for the toxicity of substituted phenols, anilines and nitrobenzenes to algae (Scenedesmus obliquus) have been studied. Chemicals were divided into polar narcotics and electrophiles based on the structure criteria according to the toxicity mechanisms of action. A good relationship between the toxicity and octanol / water partition coefficient (logP) was observed for the polar narcotic compounds. The results clear that the hydrophobicity is the determining physicochemical parameter in modeling narcotics. However, no significant significant mono-parametric QSAR models could be made from descriptors calculated in this study for all the compounds. In order to investigate the mechanisms of toxic action and develop QSAR models for all compounds, Abraham solvation descriptors were calculated from the program of Pharma-Algorithms. Stepwise regression produced a three-parameter QSAR model (polarizability / dipolarity, hydrogen-bond basicity and mo lecular volume with a good statistical fit for all the compounds studied, which had square of the correlation coefficient R2 = 0.83. We have also developed an interpretable QSAR model by using parameter of logP, which represents the bio-uptake process, and polarizability / dipolarity (S), which represents the interaction of chemicals with the acceptor micromolecules (target receptor) at the active site. No hydrogen-bond interaction was observed between the chemicals and receptor micromolecules.