Full geometric optimization of bicyclo[3.2.2]nona-6,8-diene (BND) has been done by semiempirical and ab initio methods and the structure of the molecule has also been investigated. The double bond (I) situated in the opposite direction of methylene group in BND molecule is more exo pyramidalized than the other double bond (II). The electron density (q(i),(HOMO)) of the double bond(I) in HOMO of the molecule is more than that of the (II) double bond. Exo and endo faces of exo pyramidalized double bonds of the molecule are not equal and electron density is higher-in endo faces. The molecular complexes of BND with bromine have been investigated by AM1 method and their stable configurations determined. The reason for endo molecular complexes being more stable than exo is that the stability is caused by electronic and steric factors. Because of electronic factors, BND...Br-2(endo1) complex is more stable than BND...Br-2 (endo 2). The endo-bridged bromonium cation(I) is relatively more stable than the endo-bridged cation(IV). Endo-facial stereoselectivity and regioselectivity should be observed in the addition of bromine to BND molecule. Endo-facial stereoselectivity is caused by electronic and steric effects, regioselectivity by electronic effects. The rearranged bromocarbonium cation(V) is the most stable among the cationic intermediates and the ionic addition reaction occurs via this cation.