Egg colors and patterns have long been of interest for ornithologists and evolutionary biologists, with several hypotheses proposed to explain them. These include: Wallace's hypothesis, the structure hypothesis, the brood parasitism hypothesis and the post-mating sexual selection signal hypothesis. However, none of these are sufficient to elucidate the evolutionary mechanism involved. In this study, egg polymorphism and phylogenetic relationships within the avian family Paradoxornithidae were investigated. When compared with phylogenetic information, we found that egg color matched two size-related clades within the Paradoxornithidae. The larger parrotbills all lay patterned eggs with pale background colors, whereas the smaller parrotbills lay plain pale blue eggs. To our knowledge, this is the first study to detect such a relationship between egg color and pattern and phylogeny in parrotbills, suggesting that they are under strong phylogenetic constraints and can be treated as an important indicator of phylogenetic relationship.