BACKGROUND: A POLYMER BLEND (POLYMER MIXTURE) COMPOSED OF AT LEAST TWO POLYMERS, CREATES A NEW MATERIAL WITH DIFFERENT PHYSICAL PROPERTIES, THEIR RESULT IS CALLED AS COPOLYMER. VIRTUALLY ALL IMPORTANT PROPERTIES INCLUDING THERMO PHYSICAL AND MECHANICAL PROPERTIES (ESPECIALLY IMPACT STRENGTH), THERMALST ABILITY, AND PRICE CAN BE IMPROVED IN THIS WAY [1]. IN RECENT YEARS, ARTIFICIAL NEURAL NETWORKS (ANN) HAVE ATTRACTED MORE ATTENTION. ANN MODELING OF COMPLEX NONLINEAR SYSTEMS WAS VERY SUCCESSFUL. THE ADVANTAGES OF THIS METHOD COMPARED WITH THE CONCEPTUAL MODELS, THE HIGH SPEED, SIMPLY AND HIGH CAPACITY THAT REDUCES ENGINEERING [2]. THE PRESENT WORK IS AN ATTEMPT TO USE ARTIFICIAL NEURAL NETWORKS TO DETERMINE THE DENSITY OF POLY (ETHYLENE-CO-VINYL ACETATE).METHODS: THE MOST COMMON NEURAL NETWORK APPROACH IN SOLVING PROBLEMS IS MULTILAYER PERCEPTRONS (MLP) [1]. AN ARTIFICIAL NEURAL NETWORK OF MLP TYPE, WERE DESIGNED TO DETERMINE THE DENSITY OF THEPOLY (ETHYLENECO- VINYL ACETATE).RESULTS: IN THE CURRENT STUDY, THE TEMPERATURE (T), PRESSURE (P), MOLECULAR WEIGHT (MW) AND COMPOSITION (XI) ARE USED AS INPUT VARIABLES. FOR THIS STUDY, THE ABSOLUTE AVERAGE RELATIVE ERROR (MSE) WAS CHOSEN AS A MEASURE OF THE PERFORMANCE OF THE NET. THE NET WITH ONE HIDDEN LAYER (13 NEURONS) WITH MEAN SQUARE ERROR OF 8.1×10-2 LEAD TO THE BEST PREDICTION SHOWS.CONCLUSION: THE RESULTS SHOWED THAT AN ANN WITH OPTIMUM TOPOLOGY (4-13-1) HAS A GOOD ACCURACY (AAD%=8.008×10-5»0) AND CORRELATION COEFFICIENT (R2=1) TO ESTIMATE DENSITY OF PE-CO-VA (1988 DATA POINT). THE FINDINGS DEMONSTRATED THAT THIS ANN IS A PROFICIENT METHOD AND HAS BETTER ACCURACY.