Comparative studies have been made on the mechanical properties of High density polyethylene/polypropylene (HDPE : PP) and Low density polyethylene/polypropylene (LDPE : PP) binary blends. Morphological analysis has been also performed using SEM. Blends have been prepared by melt mixing in an extruder. Mechanical tests were performed on the two groups of binary blends. Binary blends (HDPE : PP) gave higher values of tensile strength, fracture strength, young modulus, hardness, creep rate and creep modulus than LDPE : PP. The blend of ratio 20%HDPE : 80%PP shows superior mechanical properties, this blend could bear a load of 846.9 N with an extension of 3.94 mm. SEM results indicated that 20HDPE : 80PP and 20LDPE : 80PP are immiscible blends.