PURPOSE: To obtain the rein composition which can produce a prepreg that is excellent in storage atability at room temperature, is capable of being molded at relatively low temperatures, and causes no defects on the ground surface of its molded articles by incorporating a low-temperature-active potential curing agent and a specific whisker in an epoxy resin.

CONSTITUTION: This epoxy resin composition for prepreg is prepared by mixing 100 pts.wt. of an epoxy resin (A), 3-60 pts.wt. of a low-temperature-active potential curing agent (B) (e.g. an amine-adduct potential curing agent and a microcapsule potential curing agent of a diaphragm-breaking type, which are activated at about 80°C) and 0.05-30 pts.wt. of a whisker (C) with an aspect ratio of 3-500. The prepreg prepared from this resin composition has a proper workability and excellent composite characteristics, is excellent in storage stability at room temperature, is capable of being molded at a relatively low temperature around 80°C, produces no wastes upon molding, and causes no defects on the ground and coating surface of its molded articles.