Allopurinol USP batches of same size, method, equipment and validation criterion were taken. The critical process parameter involved were reaction, drying, milling, sifting, milling, and blending stages were validation. Quality cannot be assured by daily quality control testing because of the limitations of statistical samples, and the limited facilities of finished product testing. Validation checks the accuracy and reliability of process. Aim of this work was to study prospective process validation of allopurinol USP designed to meet the current regulatory requirements and prove with assurance that the product meets the predetermined specifications and quality attributes. The critical process parameter was identified with the help of process capability and evaluated by challenging its in house and compendial specification. Three initial process validations batches APL/008, APL/009 and APL/010 were identified and evaluated as per validation master plan. The outcome indicated that this process validation data provides high degree of assurance so that manufacturing process produces a quality product.