Provided is a surface-treated spinel particle (B) including a spinel particle (A) including a magnesium atom, an aluminum atom, and an oxygen atom and a surface treatment layer disposed at least a portion of the surface of the spinel particle (A). The surface treatment layer includes a surface-treating agent including an organic compound or a cured product of the surface-treating agent. The spinel particle (A) further includes molybdenum. The crystallite diameter of the [111] plane of the spinel particle (A) is 220 nm or more. Also provided are a method for producing the surface-treated spinel particle (B), a resin composition including the surface-treated spinel particle (B), and a molded article.