Abstarct: In the first section of this thesis two novel methods of spectrophotometry were presented for simultaneous determination of Catechol (Cat) and hydroquinone (Hyd) .In the second section ,same methods were considered for simultaneous determination of Resorcinol (Res) and hydroquinone )Hyd(. Novel methods of spectrophotometry extended ratio subtraction (EXRSM), simultaneous ratio subtraction (SRSM) are compared with partial least square (PLS). All effective factors on sensitivity of methode were considered and optimised. In the first section of this thesis, in all three methods linear range of (Cat) and (Hyd) obtained and respectively are:(1-15) and (1-12) mg L-1. In the second section, for all three methods linear range of (Res) and (Hyd) obtained and respectively are:(1-15) and (1-12) mg L-1. In the first section, in all three methods (EXRSM, SRSM, PLS ) detection limit of (Cat) obtained and respectively are 0.169,0.074 and 0.216 mg L-1 and detection limit of (Hyd) obtained and respectively are 0.132, 0.132, 0.243 mg L-1. In the second section, in all three methods (EXRSM, SRSM, PLS) detection limit of (Res) obtained and respectively are 0.168,0.101 and 0.108 mg L-1 and detection limit of (Hyd) obtained and respectively are 0.132, 0.132, 0.139 mg L-1 .Influence of diffrent interferences on selectivity of methods are considered. All proposed methods have admissible precision and accuracy for determination of Cat and Hyd and that of Res and Hyd in their binary mixtures exist in tap water.