An experimental investigation of the explosion characteristics of dust clouds of aluminum and magnesium was carried out for a wide range of dust concentrations up to 7000 g/m 3, using a new closed experimental apparatus. The explosion characteristics of aluminum and magnesium did not show much difference. The explosion pressure for aluminum and magnesium tended toward maximum values at concentrations roughly 3 to 5 times higher than the stoichiometric concentrations in the reactions of Al to Al 2O 3 and Mg to MgO. The explosion pressure for aluminum decreased rapidly whereas that of magnesium decreased fairly showly with increasing dust concentration. The optimum dust concentration, at which the explosion pressure was highest, increased for aluminum and decreased for magnesium as the amount of oxygen available for the reaction decreased. The time-to-peak pressure/dust concentration curve for aluminum was convex downwards with the minimum value near the optimum dust concentration, whereas the curve for magnesium was constant after it reached the minimum. In the relation between the amount of residual oxygen and the concentration of the dust cloud, the trend was the same for both aluminum and magnesium as that of the time-to-peak pressure/dust concentration curve for magnesium. The amount of oxygen available for the reaction was changed by diluting the air with nitrogen [case (I)] and by decreasing the initial pressure [case (II)]. It was found that the explosion region of case (II) was wider with respect to both oxygen and dust concentrations than that of case (I), although the explosion pressure was higher in case (I) than in case (II), except near the explosion limit.