Overall elastic and ultrasonic properties of a unidirectional composite containing partially debonded fibres have been studied by numerical analysis. The present analysis is concerned with the effective elastic modulus for longitudinal sheer deformations and the effective wave propagation characteristics for longitudinal shear waves. First, both static and time-harmonic dynamic problems are analysed in a unified manner for a single elastic fibre partially bonded to an elastic matrix. On the basis of the single-fibre analysis, the effective shear modulus, the phase velocity and the attenuation coefficient are computed by micro-macro linking theories accounting for a statistical character of the fibre/matrix debonding occurring with a certain preferential orientation. Debonding induced variation and anisotropy in elastic and ultrasonic characteristics of the composite are discussed in detail from a viewpoint of non-destructive damage evaluation, (C) 2000 Elsevier Science Ltd. All rights reserved.