N-oxidation and subsequent ring enlargement through the Meisenheimer Rearrangement of the properly substituted tetrahydroisoquinolines yielded nine novel 7.8- dimethoxy-3-methyl-1- (substitutedphenyl)-1,3,4,5- tetrahydro-2,3-benzo[e]oxazepine derivatives. Characterization of the final products have been done by UV, EIMS. 1H and 13C NMR spectroscopy. These compounds, together with seven more analogs which have been screened for their antimicrobial activity, using the microdilution technique. The results indicate that none of the compounds possesses any significant antibacterial or antifungal activity against the microorganisms tested in this study. Keywords : 2.3 - benzo[e] oxazepines. 1,2,3,4,- tetrahydroisoquinoline N-oxides, Meisenheimer Rearrangement, ring enlargement, antimicrobial activity