Nowadays the development of composite materials has increasing importance. In this study Nextel 440 type alumina fibre reinforced aluminium matrix composite wires were investi-gated. Composite wires produced using the continuous process are suitable to simplify the introduc-tion of fibre reinforcements into aluminium castings as well as the production of double composite, sandwich and preferentially reinforced structures. This paper focuses on the porosity of composite wires because minimizing porosity is the primary condition of good mechanical properties. Compo-site wires were produced with different infiltration pressures (0.83 MPa, 1.03 MPa, 1.24 MPa, 1.52 MPa, 1.65 MPa 1.86 MPa and 2.07 MPa) and different diameters (1 mm and 2 mm) to determine the correlation between infiltration pressure and the porosity of wires. 10 grinded cross-sectional samples were made from each type of composite wires. Based on the micrographs of these samples the volume fraction of aluminium was determined by image analysis, which also yielded informa-tion on the porosity of wires. The results show that there is direct linear correlation between the infiltration pressure and the change in porosity. These findings, however, are valid only for the in-vestigated range of pressure.