In this paper, the degradation behavior under hot water of the hemp fiber reinforced thermosetting resin composite materials was examined. Especially, the effects of drying condition for hemp fiber before molding on the mechanical property and degradation behavior of the composites were investigated. In composite materials that used dry hemp nonwoven fabric, impregnation of the resin into the hemp fiber was good and cross-linkage of the resin was progressed enough. As a result, the moisture absorption by the immersion was suppressed, and a big influence was not exerted on the mechanical properties. On the other hand, in composite materials that used un-dry hemp nonwoven fabric, the resin was not impregnated sufficiently into the hemp fiber due to the moisture existed in hemp fiber and cross-linkage of the resin was not progressed enough from the result in the DSC measurement. Therefore, it is thought that the moisture absorption to the unimpregnated part was generated, and the amount of the moisture absorption by the immersion was increased. As a result, the interface between hemp fiber and the resin was deteriorated, and the mechanical properties were decreased greatly by the decrease in the interfacial property. As a consequence, it was suggested that the control of moisture absorption during molding was a very important in molding the natural fabric reinforced composite materials. In addition, the effect of the surface treatment with the Shellac resin solution on the degradation behavior under hot water was investigated for hemp nonwoven cloth reinforced unsaturated polyester composite materials was examined. In the surface treatment with the Shellac resin, the improvement of the interfacial properties between fiber and resin was not achieved, but moisture absorption was restrained.