A silicon nitride sintered body having improved wear resistance and a wear-resistant member using the silicon nitride sintered body are provided. A silicon nitride sintered body according to an embodiment includes silicon nitride crystal grains and a grain boundary phase. An average value of solid solution oxygen amounts of the silicon nitride crystal grains in a 20 μm×20 μm region at any cross section is not less than 0.2 wt %. In a 50 μm×50 μm region at any cross section, an average value of major diameters of the silicon nitride crystal grains is not less than 0.1 μm and not more than 10 μm, and an average value of aspect ratios of the silicon nitride crystal grains is not less than 1.5 and not more than 10.