Superconducting MgB2, composite wires were prepared by packing blend of MgB2 inside of Cu tubes using powder in tube (PIT) method. The produced samples of the wires were then characterised by using SEM, XRD and AC susceptibility measurements. The measured fundamental susceptibility is compared with Bean model. We have obtained an empirical functions for the penetration field H-p = H-x(1-t)(beta), where t is the reduced temperature. In addition, ac losses were calculated at the same fixed temperatures to compare theoretical solutions. There is a qualitative agreement between the experimental results and theory. (C) 2004 Elsevier B.V. All rights reserved.