INTRODUCTION Analysis of pharmaceuticals is crucial to guarantee the quality and viability of both finished pharmaceutical products and the raw materials used to make them. Isolating, identifying, and quantifying chemicals in a sample matter are all part of pharmaceutical analysis, a subfield of analytical chemistry. Its focus is on the quantitative and qualitative chemical characterization of materials. Many new methods of analysis have emerged in recent decades. The analytical method is a specific application of a technique for the purpose of issue solving. The development and assessment of new products, as well as the safeguarding of consumers and the natural environment, all rely heavily on analytical instrumentation. This equipment can only ensure the safety of our food, medicine, water, and air because it gives the lower detection thresholds needed. Validation of an analytical method is showing that the method meets certain criteria through controlled laboratory experiments, that the technique’s performance characteristics fulfill the needs of its intended analytical applications. Assay validation is critical in the pharmaceutical sector for two main reasons. The first and most crucial is assay, an essential aspect ABSTRACT New medication combinations are introduced every day. As a result, various diseases and disorders are treated using a combination of several therapeutic medicines that each have a somewhat distinct mechanism of action. Therefore, it is crucial to develop methods of analyzing medicines employing a range of methods that may be utilized. A UV 730d (dad) absorbance detector, a 20 L injection loop, a sp 930d pump, a 4.6 by 100 mL C18 column (Agilent), and Chemstation software are all included in the setup: approximately 60 water and 40% methanol (pH 3.0 adjust with OPA). Maximum efficiency was achieved when the system was operated at a wavelength of 233 nm. The procedure’s efficacy was confirmed by testing it against ICH guidelines. These techniques were found to be linear, precise, broad, and stable. The procedure was found to be easy, accurate, exact, affordable, and easy to use again and again. This means that olmesartan and hydrochlorothiazide, in both bulk form and finished products, can be tested for quality using the proposed methodologies. Keywords: HPLC, Hydrochlorothiazide, Method development, Olmesartan, Validation. International Journal of Pharmaceutical Quality Assurance (2023); DOI: 10.25258/ijpqa.14.1.07 How to cite this article: Ahmad S, Mujawar T, Pawara J, Sable V, Patil K, Tare H. Analytical Method Development and Validation for the Simultaneous Estimation of Olmesartan and Hydrochlorothiazide by RP-HPLC in Bulk and Tablet Dosage Forms. International Journal of Pharmaceutical Quality Assurance. 2023;14(1):30-35. Source of support: Nil. Conflict of interest: None Analytical Method Development and Validation for the Simultaneous Estimation of Olmesartan and Hydrochlorothiazide by RP-HPLC in Bulk and Tablet Dosage Forms Sufiyan Ahmad 1* , Tabrej Mujawar 2 , Jayashri Pawara 1 , Vijay Sable 3 , Khushabu Patil 4 , Harshal Tare 5 1* Department of Quality Assurance, Gangamai College of Pharmacy, Nagaon, Affiliated to Kavayitri Bahinabai Chaudhari North Maharashtra University, Jalgaon, Maharashtra, India. 2 Department of Pharmacology, Gangamai College of Pharmacy, Nagaon, Affiliated to Kavayitri Bahinabai Chaudhari North Maharashtra University, Jalgaon, Maharashtra, India. 3 Department of Pharmaceutics, Lokmangal College of Pharmacy, At Post–Wadala, Tal. North Solapur, Solapur, Affiliated to Dr. Babasaheb Ambedkar Technological University, Lonere, Maharashtra, India. 4 Department of Quality Assurance, Arunamai College of Pharmacy, Mamurabad, Affiliated to Kavayitri Bahinabai Chaudhari North Maharashtra University, Jalgaon, Maharashtra, India. 5 Department of Pharmacognosy, Sharadchandra Pawar College of Pharmacy, Otur, Tal. Junnar, Affiliated to Savitribai Phule Pune University, Pune, Maharashtra, India. Received: 27 th December, 2022; Revised: 17 th January, 2023; Accepted: 14 th February, 2023; Available Online: 25 th March, 2023 RESEARCH ARTICLE *Author for Correspondence: sufipharm1712@gmail.com