Coated magnesium oxide particles having high filling efficiency and high mass-productivity and suitable for a thermal conductive filler are provided, the coated magnesium oxide particles being coated magnesium oxide particles in which the surface of magnesium oxide particles is coated with at least one of a fatty acid and a fatty acid metal salt, and wherein X in relation to particles is defined as X=[a BET specific surface area diameter calculated from a BET specific surface area of the particles]÷[D50 of the particles], provided that D50 is a particle diameter at 50% accumulation in a cumulative particle size distribution of the particles, the magnesium oxide particles having X of less than 0.2 and D50 of 5 to 100 μm, and the coated magnesium oxide particles having X of 0.2 or more, D50 of 5 to 100 μm, and oil absorption of less than 25 mL/100 g.