We established a recessive cataract model from a spontaneous mutation in the KUNMING outbred mice. Lens opacity appears 11 days after birth. Slit lamp examination reveals that the opacity mainly localizes to the nuclear region of the lens. Histological analysis shows a severe degeneration of the epithelial cells underneath the anterior lens capsule, whereas those cells in the equatorial region display an excessive proliferation and migration. Within the cortical area underneath the posterior lens capsule, both vacuoles and morgagnian-like bodies are seen. Blue-stained spherical bodies are observed in the embryonic nucleus, forming a Y-like pattern. We mapped the disease locus and found a homozygous G to A nucleotide conversion at position 489 of Crygs in mutant mice, leading to a truncated gene product (Trp163Stop). This finding suggests that CRYGS is not only a lens structural protein, but is also likely to be involved in epithelial cell proliferation, apoptosis, and migration.