The present invention relates to thermochromic micro particles capable of stably implementing a high chromogenic property and a decolorization property and having an improved erasing property, thermal resistance, and chemical resistance, and a thermochromic ink composition, a writing apparatus, and a smart window using the same. The thermochromic micro particles comprise a core part including a phase change material, a dye, and a developer, the phase change material including at least one selected from the group consisting of at least one chain hydrocarbon having a carbon number of 8 or more, a hydrated inorganic salt, alcohol having a carbon number of 3 or more, and polyalkyleneglycol; and a shell layer including a polymer resin.
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