Melting mixtures of high density polyethylene (HDPE) and glycerol ester of hydrogenated rosin (ester gum) were prepared under select conditions using up to 50% of rosin. All blends showed phase separation. The size of rosin domains varied with the content of low molecular weight constituent. The 50/50 blend showed the highest dispersion and the presence of micro and macro rosin domains. Up to 20% rosin a slight decrease of Young＇s modulus was noticed while above this rosin content a slight increase occurred. The stress and elongation dropped markedly above 10% of rosin. The hardness of blends showed the same behavior as the elastic modulus. The melt now index increased exponentially with the rosin content while processability has improved.