The present invention relates to a latent heat storage material composition comprising 65 to 85 wt % of sodium sulfate decahydrate, 1 to 20 wt % of ammonium chloride and 1 to 20 wt % of sodium bromide, and optionally 1 to 20 wt % of ammonium sulfate. The composition has a melting point of 5.degree. to 10.degree. C., has large latent heat at the melting point and exhibits excellent long-term performance.
