Abstract: The photochemical behavior of photocycloaddition of dibenz (a, j) anthracene with 1, 3-cyclohexadiene in solution was described.By analyzing the butadiene-like nodal patterns of the reactants and the products about the reacting position in the frontier molecular orbitals (FMO’s), it has been deduced that the reaction may proceed in accordance with concerted mechanism.We have also found that the n⁴s + n⁴s photoadduct may undergo a photochemical rearrangement to the n⁴s + n²s photoadduct under any given set of conditions. The rearrangement is likely to proceed via a biradical intermediate which cyelizes to give the less strained product.