Calcium carbonate (CaCo3)-filled low-density polyethylene (LDPE)/linear low-density polyethylene (LLDPE) composites were fabricated by means of a twin-screw extruder, and the tensile mechanical properties of the tubing with thickness of 0.5 mm made from these composites were measured at room temperature to identify the effect of the filler concentration on the properties of these composites. The results showed that the tensile elastic modulus increased roughly linearly with increasing weight fraction (phi(f)) of the fillers. The tensile fracture strength (sigma(b)) along longitudinal direction was obviously higher than that along transverse direction under the same test conditions, especially at higher filler concentration. The values of sigma(b) of the specimens along both the two directions achieved minimum at phi(f) = 20%. Furthermore, the melt flow rate (MFR) and heat enthalpy (Delta H) of the composite materials were measured. It was found that both the MFR and the Delta H decreased with the addition of phi(f). The Delta H for the composite with LDPE/LLDPE ratio of 70/30 was higher than that of the composite with LDPE/LLDPE ratio of 50/50 at the same filler concentration, but contrary to the MFR. (c) 2007 Wiley Periodicals, Inc.