By the use of the partial least squares method and 11 fundamental quantum chemical descriptors computed from the PM3 Hamiltonian, a Quantitative Structure-Property Relationship model was obtained for direct photolysis half-lives of selected polycyclic aromatic hydrocarbons (PAHs) under irradiation of sunlight. Direct photolysis half-lives for some other PAHs without reported values were predicted. It was concluded from the model that the main factors affecting photolysis half-lives of PAHs under irradiation of sunlight are PAH absolute hardness and electronegativity, which are related to the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital, (Elumo - Ehomo) and (Elumo + Ehomo), respectively. Increasing Ehomo and the average molecular polarizability (alpha) values of the PAHs leads to decrease of photolysis half-lives. Increasing (Elumo - Ehomo) and Elumo values of the PAHs leads to an increase of the PAH photolysis half-lives.