The giant magnetoimpedance in Ti/CoP plated wires with various CoP thickness was investigated. There is an optimal thickness of CoP magnetic layer for obtaining a large magnetoimpedance. The frequency f Z where the maximum magnetoimpedance ðÁZ=Z 0 Þ max occurs, shifts to low frequency with an increase of CoP thickness. Such shift is correlated with the reduction of the effective critical frequency of skin effect, accompanying the increase of magnetic layer thickness. The magnetic anisotropy field H K for Ti/CoP composite wires depends not only on the radial distance of CoP from the axis of the wire, but also on the CoP thickness.