A sialon sintered body includes a β-sialon (Si6-ZAlZOZN8-Z) and at least one polytype sialon, wherein a Z value is 0.4 or greater and 1.0 or less, a proportion of a total of peak intensities of each polytype sialon to a total of peak intensities of each sialon, is 10% or greater and 50% or less, at least one rare earth element B selected from a group consisting of La and Ce and at least one rare earth element C selected from a group consisting of Y, Nd, Sm, Eu, Gd, Dy, Er, Yb, and Lu is included, a molar ratio of the rare earth element B and the rare earth element C is 1.0:0.06 to 1.0:3.5 in terms of an oxide, and a total content of the rare earth elements B and C is 0.8 mol % or greater and 4.0 mol % or less in terms of an oxide.