A serious problem that has been recognized recently was the environmental pollution of waste plastic, where most synthetic polymers have a resistance to degradation by microorganisms in spite of their good physicochemical properties such as transparency and flexibility and their mechanical properties. Therefore, various studies were carried out to achieve the promotion of the degradation of synthetic polymers. To overcome the problems met, different ways could be carried out; the common and active one is the polymer blends with natural polymers derived from plants or biosynthetic polymers from microorganisms which were readily decomposed in the environment during their lifetimes and enhanced the biodegradability of plastic products in landfills and composts, and the plastic must still retain all of the physical properties expected by the consumer and then, when placed in the environment, degrade more rapidly in comparison with untreated polymers. In this work two types of synthetic polymers are investigated that are of highly resistant to microbiological degradation or deterioration and are accumulating in the environment, there polymers are the high density polyethylene and polystyrene the most common plastics used in the world. The natural polymer choiced for blending was used in different percentages weight by weight [%(w/w)] of synthetic polymers in order to select the best weight percent capable to keep the physical properties on minimum level like the virgin polymers : Chitosan, Cellulose, Starch, Alginate, Pectin, Shellac and Xanthan which are the natural polymers with their hydrolysable linkages along the polymer and their stereo-orientation in chains to keep it fit to the enzyme which adds an hydrophilicity character to their nature making them bioassimilate for the microorganisms. Several types of fungus along with their extracted enzyme were used for inoculation of blended samples normally isolated from the same environments suppose waste plastic are Aspergillus niger, Aspergillus terreus, Fusarium solani, Trichoderma harziauum and Tricoderma vivide. The study includes different types of chemical, physical and mechanical analysis of the blended samples after being prepared with different percentages (2,5,10 % w/w) and inoculated with different types 2 of fungus and their enzymes and incubated at a constant conditions almost similar to that of the environmental landfill. According to the ASTM standard, the average molecular weight, inherent viscosity and the percentage weight loss was estimated before and after inoculation. FT-IR characterization of the polymers was carried out and the blend between the polymers was investigated and a new functional groups were explored which indicated a significant changes in their chemical structures that occurred after inoculation with fungi’s enzymes. The mechanical properties include stress-strain investigations, Young’s modulus and elongation at break pointed to a decrease in the mechanical properties of the blended plastic films after incubation with the microorganisms for three months. Thermal studies of the blended polymers indicated that the percentages of weight loss decrease with temperature increase in thermogravimetrical analysis (TG) after inoculation with fungi’s enzymes and their percentage crystallinity were decreased due to the difficulties of polymer chains rearrangement after polymer chains cleavage because of fungi’s cultured. The SEM micrographs show the homogeneous blending between the polymers, and also explained the long cracks with deep cleavages after germination of fungi’s colonies along the film surface. The above investigation was concluded depending on the evidences that HDPE and PS polymers were biodegraded after inoculated with microorganisms and incubated for three months or enzyme solution and incubated for one month at a convenient conditions with the help of blended natural polymers.