Three types of unidirectional carbon fiber/PEEK composites are fabricated from : (a) prepreg sheet, (b) plain weave cloth ; warp : commingled yarn (1800 d) of carbon fiber with PEEK fiber, weft : PEEK yarn (70 d), (c) 5-shaft sateen weave cloth ; warp : carbon yarn (1800 d), weft : PEEK yarn (900 d). The transverse tensile properties are measured and compared with the theoretical predictions based on the perfect adhesion and interfacial slippage models. The transverse Young's moduli of the composites fabricated from (a) and (b) are in good agreement with the theoretical values based on the perfect adhesion model at the fiber/matrix interface. On the other hand, Young's modulus of the composite from (c) rather coincides with the prediction by the interfacial slippage model. The wettability and the interfacial adhesion between the carbon fiber and the PEEK resin are also investigated by the SEM observation of the fracture surface.