A hexagonal boron nitride (hBN) powder containing an aggregate of primary particles of hBN, in which the powder has a primary particle size of less than 10 µm, a ratio of an average longer diameter (L 1 ) to an average thickness (d 1 ) of the primary particles, [L 1 /d 1 ], of 5.0 or more and 20 or less, and a BET specific surface area of less than 10 m 2 /g, and the powder has one maximum peak in a range of a particle size of 45 µm or more and 150 µm or less in a particle size distribution curve of a hexagonal boron nitride powder classified to have a particle size of 45 µm or more and 106 µm or less, and has a decrease rate of the maximum peak of 10% or more and less than 40% when a dispersion liquid obtained by dispersing the hexagonal boron nitride powder in water is subjected to an ultrasonic treatment for 1 minute, the peak decrease rate being calculated by expression (1), a method for producing the hBN powder, and a resin composition and a resin sheet each containing the hBN powder.