A method of manufacturing a honeycomb structure of thermostructural composite material comprising a fiber reinforcing fabric densified by a matrix, the fibers of the reinforcing fabric being of a material selected from carbon and ceramics, as is the matrix, the method comprising the following steps:making a three-dimensional fiber fabric by means of superposed two-dimensional plies that are bonded together by means of fibers passing through the plies;making slit-shaped cuts in a staggered configuration through the plies, and through the entire thickness of the fabric;stretching the cut fabric in a direction that is not parallel to the cuts but that is parallel to the plies so as to form cells whose walls are constituted by the lips of the cuts; andwhile the cut texture is held in the stretched state, densifying it using the matrix-constituting material to obtain a rigid honeycomb structure of thermostructural material.