Phase transfer catalysed oxidation of benzaldehyde and substituted benzaldehydes by permanganate ion have been studied in non-polar solvents like ethyl acetate and toluene. The obtained products were charecterised by melting point determination and infrared spectral analysis. Benzoic acid and corresponding substituted benzoic acids were formed as the product with very high yield. The oxidation reactions were carried out by using various quaternary ammonium and phosphonium salts as phase transfer catalyst. The effect of non-polar solvents and various phase transfer catalysts on yield of product was also carried out.