The present invention addresses the problem of providing agglomerated boron nitride particles which are suitable to be used as a thermally conductive filler for a heat dissipation sheet of a power semiconductor device, and which exhibit excellent isotropy of thermal conductivity, excellent degradation resistance, and excellent kneadability with respect to resin. These agglomerated boron nitride particles (hereafter referred to as "agglomerated BN particles") are obtained by agglomerating boron nitride primary particles (hereafter referred to as "BN primary particles"). The agglomerated BN particles are characterized in that: the peak area intensity ratio ((100)/(004)) of the (100) plane to the (004) plane of the BN primary particles is at least 0.25, said peak area intensity ratio being obtained by subjecting, to a powder X-ray diffraction measurement, a pellet-shaped sample moulded at a moulding pressure of 0.85 ton/cm2 using a 10 mm phi powder pellet moulding machine; and the average crystallite diameter of the BN primary particles obtained from the (002) plane peak of the BN primary particles is at least 375 A, said average crystallite diameter being obtained as a result of filling a glass sample plate having a depth of 0.2 mm with the agglomerated BN particles such that the surface becomes smooth, and subjecting the agglomerated BN particles to a powder X-ray diffraction measurement.