Provided are a surface treated phosphor having high dispersibility and remarkably improved moisture resistance without degradation in fluorescence properties, and a method of producing the surface treated phosphor.The present invention relates to a surface treated phosphor including: a phosphor matrix including an alkaline earth metal and silicon; and a surface treatment layer including an alkaline earth metal, silicon, and a specific element belonging to groups 4 to 6 of the periodic table, wherein, when element distribution of the surface treatment layer in the thickness direction viewed in cross-section is determined by electron microscopy and energy dispersive X-ray spectroscopy coupled with the electron microscopy, the position representing the maximum peak of a specific element content is located closer to the surface than the position representing the maximum peak of a silicon content and silicon contents of the phosphor matrix and the surface treatment layer satisfy the following formula (1): [Formula 1] S1