Thermal difrusivity is one of the important physical properties of composite materials, no matter it is used as structural or functional elements. The determination of thermal diffusivity of composite is important. Copper-Carbon and Silver-Carbon fiber composites (here after Cu-Cf and Ag-Cf) possess the properties of both of Cu and Carbon fiber. The properties of the composite are adjusted within a certain range by changing the volume and/or arrangement of carbon fiber. Thus to study the thermal difrusivity of Cu-Cf as a function of the volume fraction and the arrangement of Carbon fiber is significant for seeking the condition of that the composite with light weight, high strength, appropriate thermal diffusivity and electrical conductivity, for example, it is possible to make Cu-Cf near to metal element Mo. ‘Mirage effect’ method used first by Kuo et. al.[1] is a useful tool for determination thermal diffusivity of materials. The advantages of it are local, contactless and sensitive. So far, the value of thermal difrusivity for isotropic materials from the lowest value 5 10E-5 cm 2/ s of polymer to the highest 18.5 cm2/s of diamond respectively were obtained by Kuo et. al.[2,3]. The anisotropic thermal difrusivity was measured by Zhang et. al.[4]. However few of the reports are related to composites [5].