A hexagonal boron nitride powder having an average longer diameter (L) of primary particles in the hexagonal boron nitride powder of 10 μm or less, an average thickness (D) of the primary particles in the hexagonal boron nitride powder of 0.20 μm or more, a ratio of the average longer diameter (L) to the average thickness (D), [L/D], of 3.0 or more and 5.0 or less, and a content of primary particles having a ratio of a longer diameter (l) to a thickness (d), [l/d], of 3.0 or more and 5.0 or less of 25% or more. Also disclosed is a method for producing the hexagonal boron nitride powder, and a resin composition and a resin sheet each containing the hexagonal boron nitride powder.