This paper presents a careful study and analysis of an existing manual sales and inventory control system of a pharmaceutical store and aimed at designing and developing a computer-based system in order to increase the efficiency and accuracy of the business operations of the pharmaceutical store. The study was carried out to reduce the problems of inconsistency and inaccuracy of sales and drug data inherent in the existing manual system of the pharmacy. An analysis of the current manual system was done to get a better understanding of the system. The Rapid Application Development (RAD) methodology was used in this work to implement an iterative program which is suitable for stand-alone applications that can be updated from time to time as may be required by the computer -based system. Testing was done in every phase of the development life cycle to ensure that the new system works properly. The software was developed and implemented using Visual Basic 6.0 programming language and Microsoft Access for the database platform. The software developed provides alert of every expired drug and minimum quantity of each drug available in stock. Other activities such as product sales, drugs and users registration, and periodic reports generation can also be carried out with the new system.