The aim of this thesis is to develop and validate sensitive, precise and accurate analytical methods for the analysis of certain drugs of different pharmacological action, namely; bisoprolol fumarate, indapamide, losartan potassium, etilefrine HCl, salbutamol sulphate, pioglitazone HCl, buspirone HCl, tiemonium methyl sulphate, doxazosin mesylate and finasteride in bulk, pharmaceutical preparations and in certain biological fluids. The thesis consists of three main parts: Part I: This part presents a brief introduction of the studied drugs with the demonstration of molecular structure, physical and pharmacological properties of the studied drugs and also a theoretical basic background review on the previous methods of the assay of the cited drugs. Part II: This part describes spectrophotometric methods using nanotechnology with a brief introduction about nanotechnology and it is divided into: Part II (A): It describes aggregation of pre-prepared metal nanoparticles and it is divided into two chapters Chapter (1): This chapter describes aggregation of gold nanoparticles for spectrophotometric determination of bisoprolol fumarate, buspirone HCl and doxazosin mesylate. Results obtained were compared with those of official and comparison methods. Chapter (2): This chapter is concerned with studying the aggregation of silver nanoparticles for spectrophotometric determination of buspirone HCl and doxazosin mesylate. Results obtained were compared with those of official and comparison methods. Part II (B): It describes in situ-preparation of metal nanoparticles and it is divided into three chapters Chapter (1): This chapter demonstrates spectrophotometric determination of etilefrine HCl , salbutamol sulphate and tiemonium methyl sulphate using surface plasmon resonance band of gold nanoparticles. Results obtained showed good agreement with those obtained by official and comparison methods. Chapter (2): This chapter describes the spectrophotometric determination of finasteride, indapamide and tiemonium methyl sulphate using surface plasmon resonance band of silver nanoparticles. The obtained results were compared with those of comparison methods. Chapter (3): This chapter is concerned with indirect spectrophotometric determination of bisoprolol and losartan potassium in pure form and pharmaceutical formulations using silver nanoparticles. The data given are statistically compared with those of official and comparison methods. Part III: This part describes two different methods for simultaneous determination of losartan potassium and pioglitazone HCl with a brief introduction about diabetes and hypertension combination and it is divided into two chapters: Chapter (1): This chapter demonstrates multivariate chemometric-assisted spectrophotometric methods for simultaneous determination of losartan potassium and pioglitazone HCl. Results obtained were compared with those of official and comparison methods. Chapter (2): This chapter is concerned with high performance liquid chromatographic estimation of losartan potassium and pioglitazone HCl. The data given are statistically compared with those of official and comparison methods