Vinous-throated Parrotbills and Daurian Redstarts are the major host species of Common Cuckoos in Korea. Here, we report egg color polymorphism observed in Common Cuckoos and these specific hosts. Two morphs of Common Cuckoo eggs (immaculate blue and pale blue) were found in the nests of Vinous-throated Parrotbills, and a single morph (pale blue with firebrick squiggles) was identified in the nests of Daurian Redstarts. Moreover, three egg morphs (immaculate blue, pale blue, and white) were found in the nests of Vinous-throated Parrotbills, and two morphs (pale blue with firebrick spots and pinkish-white with firebrick spots) were observed in the nests of Daurian Redstarts.