Injection moulding is one of the most popular polymer processing methods due to its high production rate as well as its ability to produce very intricate geometries at very cheaper cost and within few seconds. There are several flaws which occur while producing plastics parts by injection moulding like warpage, shrinkage, flash, sink marks etc. Shrinkage is one of the most critical problems which cause dimensional changes in the parts during the moulding process. Shrinkage can be minimized by optimal process parameters on injection moulding machine. In this study, optimal injection moulding conditions for minimum shrinkage during moulding are found by DOE Technique of TAGUCHI and ASTM D955. This experiment will help us to study the shrinkage behavior of above plastic materials and both these materials can be processed in a single mould to get the moulding with close tolerance by adding average shrinkage allowance 2% in the cavity in order to know the dimensional difference of both NYLON -66& HDPE product. Taguchi method is used to investigate the effects of melting temperature, injection pressure, holding pressure and cooling time on shrinkage of HDPE & NYLON-66 products.